hwmon: (ibmpowernv) Quieten when probing finds no device

Because we build kernels with drivers built in for many platforms, it's
normal for the ibmpowernv driver to be loaded on systems that don't have
the appropriate hardware.

Currently the driver spams the log with:

  ibmpowernv ibmpowernv.0: Opal node 'sensors' not found
  ibmpowernv: Platfrom driver probe failed

But there is no error, this machine is not a powernv and doesn't have
the hardware. So change the sensors message to dev_dbg(), and only print
an error about the probe failing if it's not ENODEV.

Also fix the spelling of "Platfrom" and print the actual error value.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Reviewed-by: Jean Delvare <jdelvare@suse.de>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>