nir: move ALU instruction before the jump instruction

nir: move ALU instruction before the jump instruction

opt_split_alu_of_phi moves ALU instruction to the end of continue block.

But if the continue block ends with a jump instruction (an explicit
"continue" instruction) then the ALU must be inserted before the jump,
as it is illegal to add instructions after the jump.

CC: Ian Romanick <ian.d.romanick@intel.com>
Fixes: 0881e90c099 ("nir: Split ALU instructions in loops that read phis")
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>