drm/amdkfd: Delete unnecessary pr_fmt switch

Given amdkfd.ko has been merged into amdgpu.ko, this switch is no
longer useful.

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