ALSA: memalloc: Fix a typo in snd_dma_buffer_sync() description

It caused a warning for kernel-doc build.

Fixes: a25684a9 ("ALSA: memalloc: Support for non-contiguous page allocation")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Link: https://lore.kernel.org/r/20211019165402.4fa82c38@canb.auug.org.au
Link: https://lore.kernel.org/r/20211019060536.26089-2-tiwai@suse.de


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