[Sparc] Use the correct encoding for ta 3

Summary: The old encoding generated a "tn %g1 + 3" instruction instead
of the expected "ta 3".

Reviewers: venkatra, jyknight

Reviewed By: jyknight

Subscribers: fedor.sergeev, jrtc27, llvm-commits

Differential Revision: https://reviews.llvm.org/D49171

llvm-svn: 337165