media: coda: Add check for kmalloc

As the kmalloc may return NULL pointer,
it should be better to check the return value
in order to avoid NULL poineter dereference,
same as the others.

Fixes: cb1d3a33

 ("[media] coda: add CODA7541 JPEG support")
Signed-off-by: Jiasheng Jiang <jiasheng@iscas.ac.cn>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>