mux: adgs1408: Add mod_devicetable.h and remove of_match_ptr

Enables probing via the ACPI PRP0001 route but more is mostly about
removing examples of this that might get copied into new drivers.

Also fixes
  drivers/mux/adgs1408.c:112:34: warning: unused variable 'adgs1408_of_match
as has been reported recently.

Fixes: e9e40543 ("spi: Add generic SPI multiplexer")
Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Peter Rosin <peda@axentia.se>
Link: https://lore.kernel.org/r/20200529145726.5708-1-peda@axentia.se


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>