exec: fix writing to MMIO area with non-power-of-two length
The problem is introduced by commit
2332616 (exec: Support 64-bit
operations in address_space_rw, 2013-07-08). Before that commit,
memory_access_size would only return 1/2/4.
Since alignment is already handled above, reduce l to the largest
power of two that is smaller than l.
Cc: qemu-stable@nongnu.org
Reported-by: Oleksii Shevchuk <alxchk@gmail.com>
Tested-by: Oleksii Shevchuk <alxchk@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>