drm/amdkfd: Fix the memory overrun

Fix the memory overrun issue caused by wrong array size.

Signed-off-by: Ma Jun <Jun.Ma2@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reported-by: coverity-bot <keescook+coverity-bot@chromium.org>
Addresses-Coverity-ID: 1527133 ("Memory - corruptions")
Fixes: c0cc999f ("drm/amdkfd: Fix the warning of array-index-out-of-bounds")
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>