drm/msm: dpu: Remove crtc_lock

Each time it's called we're holding the crtc modeset lock, so it's
redundant.

Changes in v2:
- None

Reviewed-by: Jeykumar Sankaran <jsanka@codeaurora.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>

Signed-off-by: Rob Clark <robdclark@gmail.com>