kselftest: alsa: optimization for SNDRV_CTL_ELEM_ACCESS_VOLATILE

The volatile attribute of control element means that the hardware can
voluntarily change the state of control element independent of any
operation by software. ALSA control core necessarily sends notification
to userspace subscribers for any change from userspace application, while
it doesn't for the hardware's voluntary change.

This commit adds optimization for the attribute. Even if read value is
different from written value, the test reports success as long as the
target control element has the attribute. On the other hand, the
difference is itself reported for developers' convenience.

Signed-off-by: Takashi Sakamoto <[email protected]>
Link: https://lore.kernel.org/r/Ya7TAHdMe9i41bsC@workstation
[Fix comment style as suggested by Shuah -- broonie]
Reviewed-by: Shuah Khan <[email protected]>
Signed-off-by: Mark Brown <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Takashi Iwai <[email protected]>

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