[ALSA] soc/sh: let SND_SOC_PCM_SH7760 depend on SH_DMABRG

Let SND_SOC_PCM_SH7760 depend on SH_DMABRG rather than select'ing it.
Gets rid of the Kbuild warning about SH_DMABRG being undefined on non-sh
builds.

Signed-off-by: Manuel Lauss <mano@roarinelk.homelinux.net>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>