crypto: atmel - Fix sparse endianness warnings

The param2 member in atmel_i2c_cmd is supposed to be little-endian
but was marked as u16.  This patch changes it to a __le16 which
reveals a missing endian swap in atmel_i2c_init_read_cmd.

Another missing little-endian marking is also added in
atmel_i2c_checksum.

Fixes: 11105693 ("crypto: atmel-ecc - introduce Microchip...")
Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>