s5k3l6xx: Set noise reduction register to 0x0977 for all modes

Having it at 0x0974 makes the upper half of analog gain values
act badly (best noticeable under indoor light).
2 jobs for pureos/byzantium in 63 minutes and 2 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #357131
librem5
build:aarch64

00:22:51

passed #357132
librem5:arm64
build:deb

01:03:02