ALSA: pcm - fix mmap capability check for the snd-dummy driver

The snd-dummy driver (fake_buffer configuration) uses the ops->page
callback for the mmap operations. Allow mmap for this case, too.

Cc: <stable@vger.kernel.org>
Fixes: c4824ae7 ("ALSA: pcm: Fix mmap capability check")
Signed-off-by: Jaroslav Kysela <perex@perex.cz>
Link: https://lore.kernel.org/r/20210730090254.612478-1-perex@perex.cz


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