clarify origin of volume_context

The "volume context as returned by CO in CreateVolumeRequest" is
misleading in several ways:
- the volume context is return *to* the CO by the SP
- it is returned in the CreateVolumeResponse

spec.md

@@ -1207,8 +1207,8 @@ message ControllerPublishVolumeRequest {
   // `Secrets Requirements` section on how to use this field.
   map<string, string> secrets = 5 [(csi_secret) = true];
 
-  // Volume context as returned by CO in CreateVolumeRequest. This field
-  // is OPTIONAL and MUST match the volume_context of the volume
+  // Volume context as returned by SP in CreateVolumeResponse.Volume.volume_context.
+  // This field is OPTIONAL and MUST match the volume_context of the volume
   // identified by `volume_id`.
   map<string, string> volume_context = 6;
 }
@@ -1312,8 +1312,8 @@ message ValidateVolumeCapabilitiesRequest {
   // The ID of the volume to check. This field is REQUIRED.
   string volume_id = 1;
 
-  // Volume context as returned by CO in CreateVolumeRequest. This field
-  // is OPTIONAL and MUST match the volume_context of the volume
+  // Volume context as returned by SP in CreateVolumeResponse.Volume.volume_context.
+  // This field is OPTIONAL and MUST match the volume_context of the volume
   // identified by `volume_id`.
   map<string, string> volume_context = 2;
 
@@ -1958,8 +1958,8 @@ message NodeStageVolumeRequest {
   // section on how to use this field.
   map<string, string> secrets = 5 [(csi_secret) = true];
 
-  // Volume context as returned by CO in CreateVolumeRequest. This field
-  // is OPTIONAL and MUST match the volume_context of the volume
+  // Volume context as returned by SP in CreateVolumeResponse.Volume.volume_context.
+  // This field is OPTIONAL and MUST match the volume_context of the volume
   // identified by `volume_id`.
   map<string, string> volume_context = 6;
 }
@@ -2107,8 +2107,8 @@ message NodePublishVolumeRequest {
   // section on how to use this field.
   map<string, string> secrets = 7 [(csi_secret) = true];
 
-  // Volume context as returned by CO in CreateVolumeRequest. This field
-  // is OPTIONAL and MUST match the volume_context of the volume
+  // Volume context as returned by SP in CreateVolumeResponse.Volume.volume_context.
+  // This field is OPTIONAL and MUST match the volume_context of the volume
   // identified by `volume_id`.
   map<string, string> volume_context = 8;
 }