ALSA: PCM: Remove redundant null check before kfree

kfree on a null pointer is a no-op.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
ALSA: pcm: Fix return code in pcm_native.c

Return the value obtained from snd_pcm_hw_constraint_minmax() instead
of -EINVAL. Silences the following smatch warning:
sound/core/pcm_native.c:2003 snd_pcm_hw_constraints_complete() info:
why not propagate 'err' from snd_pcm_hw_constraint_minmax() instead of -22?

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>