Multirotor WP speed fix when altitude enforce enabled

[breadoven]

Closes #9052.

Still needs testing.

[Jetrell]

@breadoven Tested and works well now.
I set a reasonable altitude difference between WP 1 and WP 2, with both being in close proximity. To see how it would react to the change in altitude... It proceeded to Adjust WP Altitude before moving to next WP... With no evidence of it trying to enter a PH_time as before, based on the Speed set point.
Both Altitude and Speed changes, based on pitch angle, were observed throughout the mission. So that worked fine too,

[breadoven]

OK, simple fix so expected it to work, thanks for confirming.