MAINTAINERS: update designated reviewer entry for MSM DRM driver

Adding myself as a designated reviewer to assist with the
code reviews for the changes coming into MSM DRM.

Acked-by: Rob Clark <robdclark@gmail.com>
Signed-off-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Link: https://lore.kernel.org/r/1637394371-16783-1-git-send-email-quic_abhinavk@quicinc.com


Signed-off-by: Rob Clark <robdclark@chromium.org>