drm/radeon: no need to check all relocs for duplicates

Only check the previously checked relocs for
duplicates. Also leaving the handle uninitialized
isn't such a good idea.

Signed-off-by: Christian König <deathsimple@vodafone.de>
Reviewed-by: Jerome Glisse <jglisse@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>