MIPS: Netlogic: Disable writing IRT for disabled blocks

If the device header of a block is not present, return invalid IRT
value so that we do not program an incorrect offset.

Signed-off-by: Jayachandran C <jchandra@broadcom.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/8882/


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