ALSA: usb-audio: Fix incorrect size check for processing/extension units
The recently introduced unit descriptor validation had some bug for
processing and extension units, it counts a bControlSize byte twice so
it expected a bigger size than it should have been. This seems
resulting in a probe error on a few devices.
Fix the calculation for proper checks of PU and EU.
Fixes: 57f8770620 ("ALSA: usb-audio: More validations of descriptor units")
Signed-off-by: Takashi Iwai <email@example.com>