hwmon: (adm1266) Set `can_sleep` flag for GPIO chip

The adm1266 driver uses I2C bus access in its GPIO chip `set` and `get`
implementation. This means these functions can sleep and the GPIO chip
should set the `can_sleep` property to true.

This will ensure that a warning is printed when trying to set or get the
GPIO value from a context that potentially can't sleep.

Fixes: d98dfad3

 ("hwmon: (pmbus/adm1266) Add support for GPIOs")
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Link: https://lore.kernel.org/r/20230314093146.2443845-1-lars@metafoo.de
Signed-off-by: Guenter Roeck <linux@roeck-us.net>