charger-manager: Use replacement variable to check state of battery

This patch remove unnecessary variable(cm->fullbatt_vchk_uV) by using
'desc->fullbatt_uV' field directly in fullbatt_handler() function
to check the state of battery.

Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Myungjoo Ham <myungjoo.ham@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>