Improves readability of qla_mbx.c.

Link: https://lore.kernel.org/r/20200805200546.22497-1-ematsumiya@suse.deReviewed-by: Himanshu Madhani <himanshu.madhani@oracle.com>
Reviewed-by: Roman Bolshakov <r.bolshakov@yadro.com>
Signed-off-by: Enzo Matsumiya <ematsumiya@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>