arm64: dts: librem5-devkit: Use a less generic codec name

The codec is currently named after the chip but it should be named like
the device itself since otherwise it's impossible to distinguish it from
other devices using the same codec (e.g. in alsa's UCM).

Signed-off-by: Guido Günther <agx@sigxcpu.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>