ALSA: pcm: Remove snd_pcm_lib_preallocate_dma_free()

Since commit d4cfb30f

 ("ALSA: pcm: Set per-card upper limit of PCM
buffer allocations") snd_pcm_lib_preallocate_dma_free() is a single line
function that has one caller, which is another single line function.

Clean this up a bit and remove snd_pcm_lib_preallocate_dma_free() and
directly call do_free_pages() from snd_pcm_lib_preallocate_free(). This is
a bit less boilerplate.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Link: https://lore.kernel.org/r/20201218153400.18394-1-lars@metafoo.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>