drm/amd/display: fix shift-out-of-bounds in CalculateVMAndRowBytes

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

drm/amd/display: fix shift-out-of-bounds in CalculateVMAndRowBytes

[WHY]

When PTEBufferSizeInRequests is zero, UBSAN reports the following

warning because dml_log2 returns an unexpected negative value:

shift exponent 4294966273 is too large for 32-bit type 'int'

[HOW]

In the case PTEBufferSizeInRequests is zero, skip the dml_log2() and

assign the result directly.