rapidio: fix error handling in mbox request/release functions

rapidio: fix error handling in mbox request/release functions

Add checking for error code returned by HW-specific mbox open routines.
Ensure that resources are properly release if failed.

This patch is applicable to kernel versions starting from v2.6.15.

Link: http://lkml.kernel.org/r/1469125134-16523-9-git-send-email-alexandre.bounine@idt.com
Signed-off-by: Alexandre Bounine <alexandre.bounine@idt.com>
Cc: Matt Porter <mporter@kernel.crashing.org>
Cc: Andre van Herk <andre.van.herk@prodrive-technologies.com>
Cc: Barry Wood <barry.wood@idt.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>