intel_scu_ipc: Oops/crash fixes

- fix reversing of command/sub arguments
- fix a crash if the i2c interface is called before the device is found

Signed-off-by: Sreedhara DS <sreedhara.ds@intel.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>