gpio/omap: fix off-mode bug: clear debounce clock enable mask on disable

gpio/omap: fix off-mode bug: clear debounce clock enable mask on disable

When debounce clocks are disabled, ensure that the banks
dbck_enable_mask is cleared also.  Otherwise, context restore on
subsequent off-mode transition will restore previous value from the
shadow copies (bank->context.debounce*) leading to mismatch state
between driver state and hardware state.

This was discovered when board code was doing

  gpio_request_one()
  gpio_set_debounce()
  gpio_free()

which was leaving the GPIO debounce settings in a confused state.
Then, enabling off mode causing bogus state to be restored, leaving
GPIO debounce enabled which then prevented the CORE powerdomain from
transitioning.

Cc: stable@kernel.org
Reported-by: Paul Walmsley <paul@pwsan.com>
Cc: Igor Grinberg <grinberg@compulab.co.il>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Acked-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Kevin Hilman <khilman@ti.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>