exec: Respect as_tranlsate_internal length clamp

exec: Respect as_tranlsate_internal length clamp

address_space_translate_internal will clamp the *plen length argument
based on the size of the memory region being queried. The iommu walker
logic in addresss_space_translate was ignoring this by discarding the
post fn call value of *plen. Fix by just always using *plen as the
length argument throughout the fn, removing the len local variable.

This fixes a bootloader bug when a single elf section spans multiple
QEMU memory regions.

Signed-off-by: Peter Crosthwaite <[email protected]>
Message-Id: <1426570554[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>