ASoC: rt5663: refine error handling

The newly added rt5663 codec driver introduces a couple of warnings
when built with -Wmaybe-uninitialized:

codecs/rt5663.c: In function 'rt5663_set_tdm_slot':
codecs/rt5663.c:2680:2: error: 'reg' may be used uninitialized in this function [-Werror=maybe-uninitialized]
codecs/rt5663.c: In function 'rt5663_set_dai_pll':
codecs/rt5663.c:2556:12: error: 'shift' may be used uninitialized in this function [-Werror=maybe-uninitialized]
codecs/rt5663.c:2596:2: error: 'mask' may be used uninitialized in this function [-Werror=maybe-uninitialized]

We can avoid those warnings by always returning an error
from the switch() statements instead of falling through
with an uninitialized variable when we hit an unexpected
case.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: df7c5216 ("ASoC: add rt5663 codec driver")
Signed-off-by: Mark Brown <broonie@kernel.org>