ALSA: pcm: Define snd_pcm_mmap_data_{open|close}() locally

snd_pcm_mmap_data_open() and _close() are defined as inline functions
in the public sound/pcm.h, but those are used only locally in
pcm_native.c, hence they should be better placed there.

Also, those are referred as callbacks, the useless inline is dropped.

Link: https://patch.msgid.link/20241113111628.17069-1-tiwai@suse.de


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