staging/rdma/hfi1: Return immediately on error

Now that the spinlock is not taken throughout hfi1_ioctl it is safe to return
early rather than setting a variable and falling through the switch.

Reviewed-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>