nau8821 driver restricts the sample rate with over sampling rate, but
currently it barely bails out at hw_params with -EINVAL error (with a
kernel message); this doesn't help for user-space to recognize which
rate can be actually used.

This patch introduces the proper hw constraint for adjusting the
available range of the sample rate depending on the OSR setup, as well
as some code cleanup, for improving the communication with
user-space.  Now applications can know the valid rate beforehand and
reduces the rate appropriately without errors.
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Link: https://lore.kernel.org/r/20220823081000.2965-2-tiwai@suse.deSigned-off-by: Mark Brown <broonie@kernel.org>