GCC4.6: Squash warning in usb_storage.c

usb_storage.c: In function ‘usb_stor_CB_reset’:
usb_storage.c:466:6: warning: variable ‘result’ set but not used
[-Wunused-but-set-variable]

Signed-off-by: Marek Vasut <marek.vasut@gmail.com>
Cc: Wolfgang Denk <wd@denx.de>
Cc: Simon Glass <sjg@chromium.org>
Cc: Mike Frysinger <vapier@gentoo.org>