scsi: arcmsr: Buffer overflow in arcmsr_iop_message_xfer()

commit 7bc2b55a5c030685b399bb65b6baa9ccc3d1f167 upstream.

We need to put an upper bound on "user_len" so the memcpy() doesn't
overflow.

Reported-by: Marco Grassi <marco.gra@gmail.com>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Tomas Henzl <thenzl@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
[bwh: Backported to 3.2:
 - Adjust context
 - Use literal 1032 insetad of ARCMSR_API_DATA_BUFLEN]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>