power: supply: max17042_battery: Prevent int underflow in set_soc_threshold

Fixes: e5f3872d ("max17042: Add support for signalling change in SOC")
Signed-off-by: Sebastian Krzyszkowiak <sebastian.krzyszkowiak@puri.sm>
2 jobs for max-irq in 67 minutes and 42 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #366633
librem5
build:aarch64

00:33:11

passed #366634
librem5:arm64
build:deb

01:07:42