The variable `mips_revision_corid' is needlessly defined global in
arch/mips/mti-malta/malta-init.c, and this patch makes it static.

Build-tested with malta_defconfig.
Signed-off-by: NDmitri Vorobiev <dmitri.vorobiev@movial.com>
Signed-off-by: NRalf Baechle <ralf@linux-mips.org>