hw/i2c: Rename i2c_realize_and_unref() as i2c_slave_realize_and_unref()

The other i2c functions are called i2c_slave_FOO(). Rename as
i2c_slave_realize_and_unref() to be consistent.

Suggested-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Corey Minyard <cminyard@mvista.com>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20200705224154.16917-4-f4bug@amsat.org>
Signed-off-by: Corey Minyard <cminyard@mvista.com>