MIPS: octeon: Fix compile error

Commit ed6a0b6e ("MIPS: octeon: Use of_address_to_resource()") lost
a cast, which causes a compile error.

Fixes: ed6a0b6e ("MIPS: octeon: Use of_address_to_resource()")
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>