[Keyboard] Fix unused variables in mschwingen modelm (qmk#10811)

Specifically, the lgreen variable isn't used, and avr-gcc 8.x complains about this. To prevent it from being an issue, just set all of these led variables to be unused.

keyboards/mschwingen/modelm/modelm.c

@@ -47,19 +47,19 @@ static cRGB led[RGBLED_NUM] = {{255, 255, 255}, {255, 255, 255}, {255, 255, 255}
 
 static const cRGB black = {.r = 0, .g = 0, .b = 0};
 
-static const cRGB green  = {.r = 0, .g = BRIGHT, .b = 0};
-static const cRGB lgreen = {.r = 0, .g = DIM, .b = 0};
+static const __attribute__((unused)) cRGB green  = {.r = 0, .g = BRIGHT, .b = 0};
+static const __attribute__((unused)) cRGB lgreen = {.r = 0, .g = DIM, .b = 0};
 
-static const cRGB red  = {.r = BRIGHT, .g = 0, .b = 0};
-static const cRGB lred = {.r = DIM, .g = 0, .b = 0};
+static const __attribute__((unused)) cRGB red  = {.r = BRIGHT, .g = 0, .b = 0};
+static const __attribute__((unused)) cRGB lred = {.r = DIM, .g = 0, .b = 0};
 
-static const cRGB blue  = {.r = 0, .g = 0, .b = BRIGHT};
-static const cRGB lblue = {.r = 0, .g = 0, .b = DIM};
+static const __attribute__((unused)) cRGB blue  = {.r = 0, .g = 0, .b = BRIGHT};
+static const __attribute__((unused)) cRGB lblue = {.r = 0, .g = 0, .b = DIM};
 
-static const cRGB turq  = {.r = 0, .g = BRIGHT, .b = BRIGHT};
-static const cRGB lturq = {.r = 0, .g = DIM, .b = DIM};
+static const __attribute__((unused)) cRGB turq  = {.r = 0, .g = BRIGHT, .b = BRIGHT};
+static const __attribute__((unused)) cRGB lturq = {.r = 0, .g = DIM, .b = DIM};
 
-static const cRGB white = {.r = BRIGHT, .g = BRIGHT, .b = BRIGHT};
+static const __attribute__((unused)) cRGB white = {.r = BRIGHT, .g = BRIGHT, .b = BRIGHT};
 
 static led_t   led_state;
 static uint8_t layer;