USB: Serial: Sierra: C597 fix

This patch is for the sierra driver and fixes a Compass 597 bug that
allows users to access the SD-Card.

This targets kernel 2.6.25-rc7

Signed-off-by: Kevin Lloyd <klloyd@sierrawireless.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>