drm/radeon: Make sure radeon_vm_bo_set_addr always unreserves the BO

Some error paths didn't unreserve the BO. This resulted in a deadlock
down the road on the next attempt to reserve the (still reserved) BO.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=90873


Cc: stable@vger.kernel.org
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Michel Dänzer <michel.daenzer@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>