dts: imx8mq-librem5: Set bq25895 thermal regulation threshold to 60°C

The default value is 120°C, meaning that bq25895 won't start limiting
charging current until its internal temperature reaches that level.
120°C seems a bit high for a handheld device, so let's reduce this
value to 60°C.
2 jobs for thermal-reg in 148 minutes and 29 seconds
Status Name Job ID Coverage
  Build
passed build:aarch64 #377180
librem5

01:01:05

passed build:deb #377181
librem5:arm64

01:27:24