ARM: dts: r8a7791: Drop _clk suffix from external CAN clock node name

The current practice is to not add _clk suffixes to clock node names in
DT, as these names are used as the actual clock names.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>