firmware: imx: scu: use EOPNOTSUPP

Per checkpatch.pl, "ENOTSUPP is not a SUSV4 error code, prefer EOPNOTSUPP"
So use EOPNOTSUPP to replace ENOTSUPP.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>