drm/amdkfd: Use kvcalloc to allocate arrays

drm/amdkfd: Use kvcalloc to allocate arrays

There were a few instances in kfd_chardev.c of kvzalloc being
used to allocate memory for an array.

Switch those to kvcalloc, which
- is the standard way of allocating a zero-initialized array
- does a check for the mul overflowing

Signed-off-by: David Francis <David.Francis@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>