ALSA: oss: remove useless NULL check before kfree

Tis patch try to remove useless NULL check before kfree

Signed-off-by: Bernard Zhao <bernard@vivo.com>
Link: https://lore.kernel.org/r/20211206014135.320720-1-bernard@vivo.com


Signed-off-by: Takashi Iwai <tiwai@suse.de>