drm/amd/pp: silence a static checker warning

This has a static checker warning because "frev" and "crev" can be
uninitialized if "info" is NULL.  I just changed the order of the checks
so that we check "info" first.

Reviewed-by: Rex Zhu <Rex.Zhu@amd.com>
Reviewed-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>