USB: misc: usb3503: Fix compiler warning

This patch fixes the compiler warning of uninitialized variable.

drivers/usb/misc/usb3503.c: In function ‘usb3503_probe’:
drivers/usb/misc/usb3503.c:215:13: warning: ‘mode’ may be used uninitialized
in this function [-Wuninitialized]

Signed-off-by: Dongjin Kim <tobetter@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>