drm/msm/dpu: Fix error pointers in dpu_plane_virtual_atomic_check

In the Linux kernel, the following vulnerability has been resolved:

drm/msm/dpu: Fix error pointers in dpu_plane_virtual_atomic_check

The function dpu_plane_virtual_atomic_check was dereferencing pointers

returned by drm_atomic_get_plane_state without checking for errors. This

could lead to undefined behavior if the function returns an error pointer.

This commit adds checks using IS_ERR to ensure that plane_state is

valid before dereferencing them.

Similar to commit da29abe71e16

("drm/amd/display: Fix error pointers in amdgpu_dm_crtc_mem_type_changed").

Patchwork: https://patchwork.freedesktop.org/patch/643132/