ALSA: usb-audio: Fix endianess in descriptor validation

I overlooked that some fields are words and need the converts from
LE in the recently added USB descriptor validation code.
This patch fixes those with the proper macro usages.

Fixes: 57f87706 ("ALSA: usb-audio: More validations of descriptor units")
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20200201080530.22390-1-tiwai@suse.de


Signed-off-by: Takashi Iwai <tiwai@suse.de>