ALSA: pcm_dmaengine: Unify two close functions

Both snd_dmaengine_pcm_close() and
snd_dmaengine_pcm_close_release_chan() are almost identical except for
a call of dma_release_channel() in the latter.  For code
simplification, unify them internally.

Just a code refactoring, and no functional changes.

Link: https://patch.msgid.link/20240625113356.2123-1-tiwai@suse.de


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