MIPS: Add default case for the FTLB enable/disable code

MIPS: Add default case for the FTLB enable/disable code

Add a default case for the FTLB enable/disable code. This will be used
to detect that something went wrong in the set_ftlb_enable() function
either because that function knows nothing about the running core, or
simply because the core can't turn its FTLB on/off.

Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/10650/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>