ab8500: Promote ab8500_fg probe before ab8500_btemp probe

ab8500_fg driver prepares instance list of fuelgauge which is required by
btemp driver for battery identification. So make sure that ab8500
fuelgauge list is ready before btemp driver starts.

Signed-off-by: Rajanikanth H.V <rajanikanth.hv@stericsson.com>
Acked-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Anton Vorontsov <anton@enomsg.org>