MIPS: Add an unreachable return statement to satisfy buggy GCCs.

It was reported that GCC-4.3.3 (with CodeSourcery extensions) fails
without this.
Reported-by: Jonas Gorski <jonas.gorski@gmail.com>
Signed-off-by: David Daney <ddaney@caviumnetworks.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/2010/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/mm/tlbex.c

@@ -109,6 +109,8 @@ static bool scratchpad_available(void)
 static int scratchpad_offset(int i)
 {
 	BUG();
+	/* Really unreachable, but evidently some GCC want this. */
+	return 0;
 }
 #endif
 /*