[SCSI] advansys: Restructure asc_execute_scsi_cmnd()

The wide and narrow boards share identical handling of the return value,
except for some trivial error messages.  Move the handling to the common
end of the function.  Also move variable declarations to the arms of
the `if' that they're used in and delete some pointless comments.

Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>