Update cve2_if_stage.sv

Created by: SylRemTHA

The variable "instr_is_compressed_out" has been removed in a previous commit but it is still called for assign next_pc. I replaced it with "instr_is_compressed" since in previous commit, "instr_is_compressed_out" was "assign instr_is_compressed_out = insert_dummy_instr ? 1'b0 : instr_is_compressed;".