sh: dwarf: Make dwarf_lookup_fde() static

arch/sh/kernel/dwarf.c:347:19: warning: no previous prototype for 'dwarf_lookup_fde' [-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/55e8261a354e8ec4d375754e404c6c1d303af715.1709326528.git.geert+renesas@glider.be


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