MIPS: Export invalid_pte_table alongside its definition

It's unclear to me why this wasn't always the case, but move the
EXPORT_SYMBOL invocation for invalid_pte_table to be alongside its
definition.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/14511/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>