usb: core: Replace hardcoded check with inline function from usb.h

Expression (urb->transfer_flags & URB_DIR_MASK) == URB_DIR_IN can be
replaced by usb_urb_dir_in(struct urb *urb) from usb.h for better
readability.

Signed-off-by: Keyur Patel <iamkeyur96@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>