ARM: dts: r8a7791: Stop grouping clocks under a "clocks" subnode

The current practice is to not group clocks under a "clocks" subnode,
but just put them together with the other on-SoC devices.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>