drm/amd/display: Refactor pageflips plane commit

[Why]
commit_planes is indented quite far

[How]
Move the pageflip code from an if statement to after a
continue

Signed-off-by: David Francis <David.Francis@amd.com>
Reviewed-by: Nicholas Kazlauskas <Nicholas.Kazlauskas@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>