ARM: shmobile: r8a7779 pinmux platform device cleanup

Use DEFINE_RES_MEM() to save a couple of lines of code.

Signed-off-by: Magnus Damm <damm@opensource.se>
[lp: Don't declare r8a7779_pfc_resources as const]
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>