[SCSI] ibmvscsi: Fix possible request_limit issue

If we encounter an error when sending a management datagram (i.e. non
SCSI command, such as virtual adapter initialization command), we
end up incrementing the request_limit, even though we don't decrement
it for these commands. Fix this up by doing this increment in
the error path for SRP commands only.

Signed-off-by: Brian King <brking@linux.vnet.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>