[PATCH, MIPS] Fix typo in N64 PLT stub

[Maciej W. Rozycki]

Maxim,

> >> Patch is OK, thanks.  Branch too please, although Tristan plans to
> >> release 2.22 this coming week.

 Your change's still missing from 2.22 (binutils-2_22-branch), please push 
it.

  Maciej