i2c: core: do not use logical device when creating irq domain

Let's rather use its physical parent device to give proper namings and
connections in debugfs.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>