mips64: fix jmpKind for BLTZ and BGEZ

As spotted by Maran Pakkirisamy, jump kind for BLTZ and BGEZ should be
Ijk_Boring and not Ijk_Call.


git-svn-id: svn://svn.valgrind.org/vex@2944 8f6e269a-dfd6-0310-a8e1-e2731360e62c