arm64: dts: r8a7795: Don't disable referenced optional scif clock

clk_get() on a disabled clock node will return -EPROBE_DEFER, which can
cause drivers to be deferred forever if such clocks are referenced in
their devices' clocks properties.

Update the disabled external scif clock node so that it
is not disabled to prevent this.

Reported-by: Jürg Billeter <j@bitron.ch>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
[simon: fix for v4.6 extracted from a larger patch targeted at v4.7]
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>