bus: fsl-mc: explicitly define the fsl_mc_command endianness

Both the header and the command parameters of the fsl_mc_command are
64-bit little-endian words. Use the appropriate type to explicitly
specify their endianness.

Signed-off-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Reviewed-by: Laurentiu Tudor <laurentiu.tudor@nxp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>