sh: mach-sh03: Make sh03_rtc_settimeofday() static

arch/sh/boards/mach-sh03/rtc.c:123:5: warning: no previous prototype for ‘sh03_rtc_settimeofday’ [-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/95417f2a3eb1561af7c2ee064efbc3ef3f03dac3.1709579038.git.geert+renesas@glider.be


Signed-off-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>