arch-arm: dtb_addr is already encoding the loadAddrOffset

arch-arm: dtb_addr is already encoding the loadAddrOffset

This fixes a bug in AArch32 where the dtb_address is
adding the loadAddrOffset twice to the dtb base address
after

https://gem5-review.googlesource.com/c/public/gem5/+/35076

Change-Id: Ia8bd35a02d998c54fbc3a889739c9abbeb506d96
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/39216
Reviewed-by: Ciro Santilli <ciro.santilli@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>