Was using the wrong prefix (gmc rather than gfx).  The function
is related to the gfx hw, not gmc.  This also makes it consistent
with the naming in gfx8.
Reviewed-by: NHarry Wentland <harry.wentland@amd.com>
Reviewed-by: NChristian König <christian.koenig@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>