radeon/r600: Fix return type in failure branch

Commit `d4e847ea` introduced a warning about making an
integer from a pointer without a cast, fix it here.

Signed-off-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
Signed-off-by: Marek Olšák <marek.olsak@amd.com>
1 file changed