When updating a tSpill/tRestore instruction to be a tSTRr/tLDRr, correctly

set up the source operands. The original instr has an immediate operand that
should be replaced with the frame reg operand rather than just adding the
reg operand. Previously, the instruction ended up with too many operands
causing an assert() when adding the default predicate. rdar://8825456

llvm-svn: 123387