usb: storage: shuttle_usbat: fix sparse warning

Fix the following sparse warning:

| drivers/usb/storage/shuttle_usbat.c:173:22: warning:
|	symbol 'usbat_usb_ids' was not declared. Should
|	it be static?

Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>