nvmem: sunxi: Check for memory allocation failure

The sunxi_sid driver doesn't check for kmalloc return status before
derefencing the returned pointer, which could lead to a NULL pointer
dereference if kmalloc failed. Check for its return code to make sure it
deosn't happen.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>