m68k: atari: Make ikbd_reset() static

When building with W=1:

    arch/m68k/atari/atakeyb.c:335:6: warning: no previous prototype for ‘ikbd_reset’ [-Wmissing-prototypes]
      335 | void ikbd_reset(void)
	  |      ^~~~~~~~~~

Fix this by making ikbd_reset() static.
There was never a user outside arch/m68k/atari/atakey.c.
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/6babf691fff55f913808ad845e66f60ab00063b2.1694613528.git.geert@linux-m68k.org

arch/m68k/atari/atakeyb.c

@@ -332,7 +332,7 @@ void ikbd_write(const char *str, int len)
 }
 
 /* Reset (without touching the clock) */
-void ikbd_reset(void)
+static void ikbd_reset(void)
 {
 	static const char cmd[2] = { 0x80, 0x01 };