gpio: ml-ioh: Use BIT() to match gpio-pch.c

The ML IOH driver is very similar to the PCH driver.  To make it more
similar, replace "1 << nr" with "BIT(nr)".  No functional change intended.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>