arch/sh/boards/board-sh7785lcr.c:298:13: warning: no previous prototype for ‘init_sh7785lcr_IRQ’ [-Wmissing-prototypes]

There are no users outside this file, so make it static.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Link: https://lore.kernel.org/r/cbe9da98a1106cdab686766e2f23f768399dbdbf.1709579038.git.geert+renesas@glider.beSigned-off-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>