drm/amd/display: remove redundant variable status

Variable status is redundant, it is being initialized with a value
that is over-written later and this is being returned immediately
after the assignment.  Clean up the code by removing status and
just returning the value returned from the call to function
dc->hwss.dmdata_status_done.

Addresses-Coverity: ("Unused value")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>