Staging: mei: fix suspend failure

wait_event_interruptible_timeout return value was wrongly used.
The remaining timeout was used as the error code.
This fix translated wait_event_interruptible_timeout return value
into error code that can be propagated.

[10291.674121] pci_pm_suspend(): mei_pci_suspend+0x0/0x8b [mei] returns 2500
It's thinkpad t400 with
00:03.0 Communication controller [0780]: Intel Corporation Mobile 4 Series Chipset MEI Controller [8086:2a44] (rev 07)

Reported-by: Arkadiusz Miskiewicz <a.miskiewicz@gmail.com>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>