Fix potential landing pad escape

If main memory contained an LPAD instruction but the incoherent I$ contained
an unrelated instruction, then the landing-pad MSBs would not have been
checked.  Fix by making the I$ coherent with the LPAD when the initial
landing-pad check is performed.

Author: aswaterman

riscv/mmu.h

@@ -346,8 +346,7 @@ class mmu_t
 
   inline insn_fetch_t load_insn(reg_t addr)
   {
-    icache_entry_t entry;
-    return refill_icache(addr, &entry)->data;
+    return refill_icache(addr, &icache[icache_index(addr)])->data;
   }
 
   std::tuple<bool, uintptr_t, reg_t> ALWAYS_INLINE access_tlb(const dtlb_entry_t* tlb, reg_t vaddr, reg_t allowed_flags = 0, reg_t required_flags = 0)