IB/rxe: Change rxe_rcv to return void

It always returns 0. Change return type to void.

Signed-off-by: Yuval Shaia <yuval.shaia@oracle.com>
Reviewed-by: Zhu Yanjun <yanjun.zhu@oracle.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Doug Ledford <dledford@redhat.com>