media: coda: jpeg: Add check for kmalloc

As kmalloc can return NULL pointer, it should be better to
check the return value and return error, same as
coda_jpeg_decode_header.

Fixes: 96f6f62c

 ("media: coda: jpeg: add CODA960 JPEG encoder support")
Signed-off-by: Jiasheng Jiang <jiasheng@iscas.ac.cn>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>