m68k: kernel: Make bad_super_trap() static

When building with W=1:

arch/m68k/kernel/traps.c:968:6: warning: no previous prototype for ‘bad_super_trap’ [-Wmissing-prototypes]
968 | void bad_super_trap (struct frame *fp)
| ^~~~~~~~~~~~~~

Fix this by making bad_super_trap() static.
There was never a user outside arch/m68k/kernel/traps.c.

Signed-off-by: Geert Uytterhoeven <[e-mail]>
Acked-by: Arnd Bergmann <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

arch/m68k/kernel/traps.c

···
  * real 68k parts, but it won't hurt either.
  */
 
-void bad_super_trap (struct frame *fp)
+static void bad_super_trap(struct frame *fp)
 {
 	int vector = (fp->ptregs.vector >> 2) & 0xff;