ALSA: usb-audio: Annotate endianess in Scarlett gen2 quirk

The Scarlett gen2 mixer quirk code defines a few record types to
communicate via USB hub, and those must be all little-endian.
This patch changes the field types to LE to annotate endianess
properly.  It also fixes the incorrect usage of leXX_to_cpu() in a
couple of places, which was caught by sparse after this change.

Fixes: 9e4d5c1b ("ALSA: usb-audio: Scarlett Gen 2 mixer interface")
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20200201080530.22390-2-tiwai@suse.de


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