MIPS: Re-use kstrtobool_from_user()

Re-use kstrtobool_from_user() instead of open coded variant.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Signed-off-by: James Hogan <jhogan@kernel.org>