FOC: Fix in kernel 'Op_cache_dma_coherent'

'Mem_unit::flush_dcache' takes void pointers as arguments, no need to take the
given void pointers ('start' and 'end') and transform them to
'Virt_addr(Address(x)' types. This breaks cache flushing in r56.

kernel/fiasco/src/kern/arm/mem_op.cpp

@@ -113,7 +113,7 @@ Mem_op::arm_mem_cache_maint(int op, void const *start, void const *end)
 
     case Op_cache_dma_coherent:
         {
-          Mem_unit::flush_dcache(Virt_addr(Address(start)), Virt_addr(Address(end)));
+          Mem_unit::flush_dcache(start, end);
           outer_cache_op(Op_cache_l2_flush, Address(start), Address(end));
         }
       break;