mptbase: fixup error handling paths in mpt_attach()

mpt_attach() was not checking for the failure to create fw_event_q.
Also, iounmap() was not being called in all error cases after ioremap()
had been called by mpt_mapresources().

Signed-off-by: Ewan D. Milne <emilne@redhat.com>
Reported-by: Insu Yun <wuninsu@gmail.com>
Reviewed-by: Tomas Henzl <thenzl@redhat.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>