Fix lint

Created by: JeanRochCoulon

@zarubaf

Sebastien Jack has detected some lint errors which break the FPGA generation in 32bits configuration. This PR fix some of them.

Git logs: load_store_unit.sv, load_unit.sv, mmu.sv, tlb.sv: fix lint warnings issue_stage.sv: fix lint warnings on rs1_forwarding and rs2_forwarding signals frontend.sv: fix lint error on icache_vaddr_q signal

A lint error related to PMP cannot be solved easily: PMP has been designed to be compliant to rv64, and not rv32. In 32bits, new registers (pmpconfig) need to be defined and current registers need to be reduced from 64 to 32bits. How can think we can fix these LINT errors? Does Moritz Schneider available to adapt the PMP to 32bits, it would be great?