ARM64: dts: meson-gx: fix gxl clock controller compatible

There are a few differences between the gxbb and gxl clock controllers
which makes them incompatible. The hdmi, gp0 and fixed pll are
different. The rate of these plls reported by gxbb driver on a gxl
device would be wrong.

Remove the gxbb compatible from the gxl clock controller node so only
the correct driver is matched.

Fixes: 973fbd55

 ("ARM64: dts: meson-gxl: Add clock nodes")
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>