i2c: meson: Fix wrong speed use from probe

Having meson_i2c_set_clk_div after i2c_add_adapter
causes issues for client drivers that try to use
the bus before the requested speed is applied.

The bus can be used just after i2c_add_adapter, so
move i2c_add_adapter to the final step as
meson_i2c_set_clk_div needs to be called before
the bus is used.

Fixes: 09af1c2f ("i2c: meson: set clock divider in probe instead of setting it for each transfer")
Signed-off-by: Lucas Tanure <tanure@linux.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>