CVE-2024-26914 drm/amd/display: fix incorrect mpc_combine array size

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

drm/amd/display: fix incorrect mpc_combine array size

[why]
MAX_SURFACES is per stream, while MAX_PLANES is per asic. The
mpc_combine is an array that records all the planes per asic. Therefore
MAX_PLANES should be used as the array size. Using MAX_SURFACES causes
array overflow when there are more than 3 planes.

[how]
Use the MAX_PLANES for the mpc_combine array size.