MIPS: Oceton: Fix build error.

If CONFIG_CAVIUM_OCTEON_LOCK_L2_TLB, CONFIG_CAVIUM_OCTEON_LOCK_L2_EXCEPTION,
CONFIG_CAVIUM_OCTEON_LOCK_L2_LOW_LEVEL_INTERRUPT and
CONFIG_CAVIUM_OCTEON_LOCK_L2_INTERRUPT are all undefined:

arch/mips/cavium-octeon/setup.c: In function ‘prom_init’:
arch/mips/cavium-octeon/setup.c:715:12: error: unused variable ‘ebase’ [-Werror=unused-variable]
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/cavium-octeon/setup.c

@@ -7,6 +7,7 @@
  * Copyright (C) 2008, 2009 Wind River Systems
  *   written by Ralf Baechle <ralf@linux-mips.org>
  */
+#include <linux/compiler.h>
 #include <linux/init.h>
 #include <linux/kernel.h>
 #include <linux/console.h>
@@ -712,7 +713,7 @@ void __init prom_init(void)
 	if (cvmx_read_csr(CVMX_L2D_FUS3) & (3ull << 34)) {
 		pr_info("Skipping L2 locking due to reduced L2 cache size\n");
 	} else {
-		uint32_t ebase = read_c0_ebase() & 0x3ffff000;
+		uint32_t __maybe_unused ebase = read_c0_ebase() & 0x3ffff000;
 #ifdef CONFIG_CAVIUM_OCTEON_LOCK_L2_TLB
 		/* TLB refill */
 		cvmx_l2c_lock_mem_region(ebase, 0x100);