lima/ppir: fix branch codegen register encode

Erico Nunes requested to merge enunes/mesa:lima-ppir-fix-branch-codegen into master

The branch instruction has 6 bits per register operand which allows it to specify a component in the register. Fix codegen so that it outputs the right component, otherwise it alwaysoutputs the x component.

This is a followup to !1372 (merged) which is where I originally hit the issue.

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