Use conservative size estimate for tBR_JTr.

Use conservative size estimate for tBR_JTr.

This pseudo-instruction contains a .align directive in its expansion, so
the total size may vary by 2 bytes.

It is too difficult to accurately keep track of this alignment
directive, just use the worst-case size instead.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@145971 91177308-0d34-0410-b5e6-96231b3b80d8