ALSA: memalloc: Drop superfluous snd_dma_buffer_sync() declaration

snd_dma_buffer_sync() is declared twice, and the one outside the ifdef
CONFIG_HAS_DMA could lead to a build error when CONFIG_HAS_DMA=n.
As it's an overlooked leftover after rebase, drop this line.

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/20211019060536.26089-1-tiwai@suse.de


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