msm_fb: display: remove old code from mdp_busy_wait

Change-Id: I178ada2864100b3954c3a0f9aafc9d75f1778cd4
Revert "msm_fb: display: return fail if pipe still staged"

This reverts commit b81388dde0fc70e01f3c650b1c5c1bda48b7738d.