gpio: qpnp-pin: Properly mask gpio get value

When gpios are set to input, we return the input buffer status
from the STATUS1 register when the 'get' gpiochip callback is
invoked. This register also includes a bit that indicates whether
the pin is enabled.

Check to verify the pin is enabled, and if it is then return the
properly masked 1-bit value. Otherwise return an error, since the
API is not valid in this state.

Change-Id: I715e17f076d0dbd67397812f98e308f863c59b7c
Signed-off-by: Michael Bohan <mbohan@codeaurora.org>