gpiolib: fix filtering out unwanted events

GPIOEVENT_REQUEST_BOTH_EDGES is not a single flag, but a binary OR of
GPIOEVENT_REQUEST_RISING_EDGE and GPIOEVENT_REQUEST_FALLING_EDGE.

The expression 'le->eflags & GPIOEVENT_REQUEST_BOTH_EDGES' we'll get
evaluated to true even if only one event type was requested.

Fix it by checking both RISING & FALLING flags explicitly.

Cc: stable@vger.kernel.org
Fixes: 61f922db

 ("gpio: userspace ABI for reading GPIO line events")
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>