i2c: mark HostNotify target address as used

I2C core handles the local target for receiving HostNotify alerts. There
is no separate driver bound to that address. That means userspace can
access it if desired, leading to further complications if controllers
are not capable of reading their own local target. Bind the local target
to the dummy driver so it will be marked as "handled by the kernel" if
the HostNotify feature is used. That protects aginst userspace access
and prevents other drivers binding to it.

Fixes: 2a71593d

 ("i2c: smbus: add core function handling SMBus host-notify")
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>