kselftest: alsa: Factor out check that values meet constraints

To simplify the code a bit and allow future reuse factor the checks that
values we read are valid out of test_ctl_get_value() into a separate
function which can be reused later. As part of this extend the test to
check all the values for the control, not just the first one.

Signed-off-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Cezary Rojewski <cezary.rojewski@intel.com>
Link: https://lore.kernel.org/r/20211217130213.3893415-2-broonie@kernel.org


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