power: supply: cw2015: correct time_to_empty units in sysfs

RRT_ALRT register holds remaining battery time in minutes therefore it
needs to be scaled accordingly when exposing TIME_TO_EMPTY via sysfs
expressed in seconds

Fixes: b4c7715c

 ("power: supply: add CellWise cw2015 fuel gauge driver")
Signed-off-by: Jan Palus <jpalus@fastmail.com>
Link: https://lore.kernel.org/r/20231111221704.5579-1-jpalus@fastmail.com
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>