gpio: gpio-vf610: do not touch other bits when set the target bit

For gpio controller contain register PDDR, when set one target bit,
current logic will clear all other bits, this is wrong. Use operator
'|=' to fix it.

Fixes: 659d8a62

 ("gpio: vf610: add imx7ulp support")
Reviewed-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Haibo Chen <haibo.chen@nxp.com>
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>