gpiolib: clear requested flag if line is invalid

gpiolib: clear requested flag if line is invalid

If `gpiochip_line_is_valid()` fails, then `-EINVAL` is returned, but
`desc->flags` will have `GPIOD_FLAG_REQUESTED` set, which will result
in subsequent calls misleadingly returning `-EBUSY`.

Fix that by clearing the flag in case of failure.

Fixes: a501624864f3 ("gpio: Respect valid_mask when requesting GPIOs")
Signed-off-by: Barnabás Pőcze <pobrn@protonmail.com>
Reviewed-by: Matti Vaittinen <mazziesaccount@gmail.com>
Link: https://patch.msgid.link/20260310204359.1202451-1-pobrn@protonmail.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>