ALSA: x86: hdmi: fix returnvar.cocci warnings

Remove unneeded variable used to store return value.

Generated by: scripts/coccinelle/misc/returnvar.cocci

CC: Jerome Anand <jerome.anand@intel.com>
Signed-off-by: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>