Using get_nasid() to find the console node will blow up nicely if

Using get_nasid() to find the console node will blow up nicely if
called on a another node than the console node, so use the master_nasid
instead and in the unlikely case that one isn't initialized yet, fall
back to get_nasid().

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