power: supply: max1720x correct capacity computation

From the datasheet of the MAX17201/17205, the LSB should be "5.0μVh/RSENSE".
The current computation sets it at 0.5mAh=5.0μVh/10mOhm, which does not take
into account the value of rsense (which is in 10µV steps) which can be
different from 10mOhm.

Change the computation to fit the specs.

Fixes: 479b6d04 ("power: supply: add support for MAX1720x standalone fuel gauge")
Signed-off-by: Thomas Antoine <t.antoine@uclouvain.be>
Link: https://lore.kernel.org/r/20250523-b4-gs101_max77759_fg-v4-1-b49904e35a34@uclouvain.be


Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>