powerpc/44x: Fix build error with -Werror for Warp platform

With -Werror enabled during the build, the warp.c file fails to build
due to the temp_isr function not containing a return statement.  This
fixes the build error and documents that the function never returns.

Signed-off-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>
diff --git a/arch/powerpc/platforms/44x/warp.c b/arch/powerpc/platforms/44x/warp.c
index 9916b39..e5c1b09 100644
--- a/arch/powerpc/platforms/44x/warp.c
+++ b/arch/powerpc/platforms/44x/warp.c
@@ -163,6 +163,9 @@
 		value ^= 1;
 		mdelay(500);
 	}
+
+	/* Not reached */
+	return IRQ_HANDLED;
 }
 
 static int pika_setup_leds(void)