drm/msm/dpu: Fix uninitialized variable

There is a possibility for an uninitialized *ret* variable to be
returned in some code paths.

Fix this by initializing *ret* to 0.

Addresses-Coverity-ID: 1642546 ("Uninitialized scalar variable")
Fixes: 774bcfb7 ("drm/msm/dpu: add support for virtual planes")
Signed-off-by: Ethan Carter Edwards <ethan@ethancedwards.com>
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/636201/
Link: https://lore.kernel.org/r/20250209-dpu-v2-1-114dfd4ebefd@ethancedwards.com


Signed-off-by: Abhinav Kumar <quic_abhinavk@quicinc.com>