USB: serial: sierra driver autopm fixes

This patch presents fixes for the autosuspend feature implementation in
sierra usb serial driver in  functions sierra_open(), sierra_close() and
stop_read_write_urbs().

The patch "sierra_close() must resume the device before it notifies it
of a closure" submitted by Oliver Neukum on Wed, October 14 has been
merged as fix in sierra_close() function.

The bug fix  in sierra_open() function restores the autopm interface
state on error condition.

The bug fix in in stop_read_write_urbs() function assures that both
receive and interrupt urbs are recycled.

Signed-off-by: Elina Pasheva <epasheva@sierrawireless.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>