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>