s5k3l6xx: Don't touch analog gain in frame regs

Otherwise it gets reset behind v4l2's back when restarting the stream.
2 jobs for s5k3l6xx in 67 minutes and 16 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #345736
librem5
build:aarch64

00:39:55

passed #345737
librem5:arm64
build:deb

01:04:36