ab8500_fg: Replace msleep() with usleep_range() for greater accuracy

Doing so provides a greater degree of accuracy when dealing with
time-frames between 1us and 20ms. msleep() is only accurate for
wake-ups greater than 20ms.

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Jonas ABERG <jonas.aberg@stericsson.com>
Reviewed-by: Johan BJORNSTEDT <johan.bjornstedt@stericsson.com>
Signed-off-by: Anton Vorontsov <anton@enomsg.org>

drivers/power/ab8500_fg.c

@@ -956,7 +956,7 @@ static int ab8500_fg_load_comp_volt_to_capacity(struct ab8500_fg *di)
 	do {
 		vbat += ab8500_fg_bat_voltage(di);
 		i++;
-		msleep(5);
+		usleep_range(5000, 6000);
 	} while (!ab8500_fg_inst_curr_done(di));
 
 	ab8500_fg_inst_curr_finalize(di, &di->inst_curr);