ALSA: compress_driver.h: include sound/core.h explicitly

Fixes the following compilation error:

   include/sound/compress_driver.h: In function ‘snd_compr_drain_notify’:
   include/sound/compress_driver.h:177:2: error: implicit declaration of function ‘snd_BUG_ON’ [-Werror=implicit-function-declaration]
     if (snd_BUG_ON(!stream))

snd_BUG_ON() is defined in sound/core.h but the file is not included explicitly,
so include it.

Signed-off-by: Qais Yousef <qais.yousef@imgtec.com>
Acked-by: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>