ARM: shmobile: alt: Correct scif2 pfc

22b16071 ("ARM: shmobile: alt: Add pfc pins to DT") introduced pfc pins
to the alt device tree but did not reference them. This patch fixes scif2
pfc by adding references to the scif2 pins.

Reported-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>