i2c: Switch .probe() to not take an id parameter

Commit b8a1a4cd ("i2c: Provide a temporary .probe_new() call-back
type") introduced a new probe callback to convert i2c init routines to
not take an i2c_device_id parameter. Now that all in-tree drivers are
converted to the temporary .probe_new() callback, .probe() can be
modified to match the desired prototype.

Now that .probe() and .probe_new() have the same semantic, they can be
defined as members of an anonymous union to save some memory and
simplify the core code a bit.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Wolfram Sang <wsa@kernel.org>