ALSA: scarlett2: Add support for reading firmware version

The 84 bytes read during initialisation step 2 were previously
ignored. This patch retrieves the firmware version from bytes 8-11,
stores it in the scarlett2_data struct, and makes it available
through a new control "Firmware Version".

Signed-off-by: Geoffrey D. Bennett <g@b4.vu>
Link: https://lore.kernel.org/r/e76cd80c3445769e60c95df12c4635fc8abfe5c7.1698342632.git.g@b4.vu


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