powerpc/4xx: Remove WatchdogHandler() to fix no previous prototype error

Building ppc40x_defconfig throws the following error:

  CC      arch/powerpc/kernel/traps.o
arch/powerpc/kernel/traps.c:2232:29: warning: no previous prototype for 'WatchdogHandler' [-Wmissing-prototypes]
 2232 | void __attribute__ ((weak)) WatchdogHandler(struct pt_regs *regs)
      |                             ^~~~~~~~~~~~~~~

This function was imported by commit 14cf11af ("powerpc: Merge
enough to start building in arch/powerpc.") as a weak function but
never defined and/or called outside traps.c

As it has only one caller fold it inside its caller and remove it.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/38fe1078eb403eef74dc8f29387636fd7ecdf43c.1692276041.git.christophe.leroy@csgroup.eu

arch/powerpc/kernel/traps.c

@@ -2225,21 +2225,10 @@ void __noreturn unrecoverable_exception(struct pt_regs *regs)
 }
 
 #if defined(CONFIG_BOOKE_WDT) || defined(CONFIG_40x)
-/*
- * Default handler for a Watchdog exception,
- * spins until a reboot occurs
- */
-void __attribute__ ((weak)) WatchdogHandler(struct pt_regs *regs)
-{
-	/* Generic WatchdogHandler, implement your own */
-	mtspr(SPRN_TCR, mfspr(SPRN_TCR)&(~TCR_WIE));
-	return;
-}
-
 DEFINE_INTERRUPT_HANDLER_NMI(WatchdogException)
 {
 	printk (KERN_EMERG "PowerPC Book-E Watchdog Exception\n");
-	WatchdogHandler(regs);
+	mtspr(SPRN_TCR, mfspr(SPRN_TCR) & ~TCR_WIE);
 	return 0;
 }
 #endif