media: amphion: delete unnecessary NULL check

vfree(NULL) is safe. NULL check before vfree() is not needed.
Delete them to simplify the code.

Generated by coccinelle script:
	scripts/coccinelle/free/ifnullfree.cocci

Signed-off-by: Ziyang Xuan <william.xuanziyang@huawei.com>
Reviewed-by: ming_qian <ming.qian@nxp.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>