Fix nfsroot build

  CC      fs/nfs/nfsroot.o
fs/nfs/nfsroot.c:131: error: tokens causes a section type conflict
make[2]: *** [fs/nfs/nfsroot.o] Error 1

This is due to mixing const and non-const content in the same section
which halfway recent gccs absolutely hate.  Fixed by dropping the const.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>