mfd: axp20x: Use dev->driver->of_match_table in axp20x_match_device()

In axp20x_match_device(), match the of_device_id table bound to the
device driver instead of pointing to axp20x_of_match directly. This
will allow us to keep axp20x_match_device() unmodified when we expand
the axp20x driver into multiple ones covering different interface
types.

of_device_get_match_data() cannot be used here as we need to know if
it failed to get a match, or if the match data value just happened to
be 0, as it is for the AXP152.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>