ARM: dts: r8a7792: remove ADSP clock

Simon Horman told me that R8A7792 has ADSP clock based on an incorrect
table in the most recent R-Car gen2 manual. But when I received that manual
I discovered that this is false: R8A7792 is the only Gen 2 SoC that doesn't
have ADSP at all.  Accordingly remove the ADSP clock from DT for the
r8a7792.

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>