ALSA: compress: Replace complex if statement with switch

A switch statement looks a bit cleaner than an if statement
spread over 3 lines, as such update this to a switch.

Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Acked-by: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>