[AsmPrinter] Fix direct callee operand lookup in CallGraphSection (#218534)
In handleCallsiteForCallgraph, direct callee operand was assumed to
always be at index 0 (MI.getOperand(0)). While true for x86_64, on
ARM Thumb/Thumb-2 (e.g. tBL), operand 0 represent predicate condition
code not the callee operand. Use getCalleeOperand to correctly retrieve
the operand.
Assisted-by: Gemini