Revert "exec: Respect as_tranlsate_internal length clamp"

This reverts commit c3c1bb9.
It causes problems with boards that declare memory regions shorter
than the registers they contain.

Reported-by: Zoltan Balaton <balaton@eik.bme.hu>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

exec.c

@@ -380,6 +380,7 @@ MemoryRegion *address_space_translate(AddressSpace *as, hwaddr addr,
     IOMMUTLBEntry iotlb;
     MemoryRegionSection *section;
     MemoryRegion *mr;
+    hwaddr len = *plen;
 
     rcu_read_lock();
     for (;;) {
@@ -394,7 +395,7 @@ MemoryRegion *address_space_translate(AddressSpace *as, hwaddr addr,
         iotlb = mr->iommu_ops->translate(mr, addr, is_write);
         addr = ((iotlb.translated_addr & ~iotlb.addr_mask)
                 | (addr & iotlb.addr_mask));
-        *plen = MIN(*plen, (addr | iotlb.addr_mask) - addr + 1);
+        len = MIN(len, (addr | iotlb.addr_mask) - addr + 1);
         if (!(iotlb.perm & (1 << is_write))) {
             mr = &io_mem_unassigned;
             break;
@@ -405,9 +406,10 @@ MemoryRegion *address_space_translate(AddressSpace *as, hwaddr addr,
 
     if (xen_enabled() && memory_access_is_direct(mr, is_write)) {
         hwaddr page = ((addr & TARGET_PAGE_MASK) + TARGET_PAGE_SIZE) - addr;
-        *plen = MIN(page, *plen);
+        len = MIN(page, len);
     }
 
+    *plen = len;
     *xlat = addr;
     rcu_read_unlock();
     return mr;