nir/lower_shader_calls: remove empty phis
This is confusing opt_cse. Signed-off-by:Lionel Landwerlin <lionel.g.landwerlin@intel.com> Fixes: 8dfb240b ("nir: Add raytracing shader call lowering pass.") Reviewed-by:
Daniel Schürmann <daniel@schuermann.dev> Part-of: <mesa/mesa!11953> (cherry picked from commit 01b0935d)