i2c: i2c-gpio: Fix GPIO output

The dm_gpio_set_dir_flags function cannot be used to update the
configuration of a GPIO pin because it does a bitwise OR with the
existing flags. Looks like commit 788ea834 ("gpio: add function
_dm_gpio_set_dir_flags") has introduced this behaviour and the i2c-gpio
driver has been broken since.

Signed-off-by: Harm Berntsen <harm.berntsen@nedap.com>
CC: Heiko Schocher <hs@denx.de>
CC: Patrick Delaunay <patrick.delaunay@st.com>