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: NJulia Lawall <julia.lawall@lip6.fr>
Signed-off-by: NFengguang Wu <fengguang.wu@intel.com>
Signed-off-by: NTakashi Iwai <tiwai@suse.de>