media: meson: vdec: potential dereference of null pointer

As the possible failure of the kzalloc(), the 'new_ts' could be NULL
pointer.
Therefore, it should be better to check it in order to avoid the
dereference of the NULL pointer.
Also, the caller esparser_queue() needs to deal with the return value of
the amvdec_add_ts().

Fixes: 876f123b ("media: meson: vdec: bring up to compliance")
Signed-off-by: Jiasheng Jiang <jiasheng@iscas.ac.cn>
Suggested-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>