xen/arm: Fix the issue in cmp_mmio_handler used in find_mmio_handler

xen/arm: Fix the issue in cmp_mmio_handler used in find_mmio_handler

This patch fixes the wrong range check done in cmp_mmio_handler().

This function returns -1 , 0 or 1  based on whether the key value
is below the range, in the range or above the range where the range is
(start, start+size). However, it should check against (start, start+size-1)
because start+size falls outside the range.

This resulted in returning a wrong mmio_handler for a given mmio address which
happened to be start+size.

This bug was introduced when the mmio region search switched from
linear search to binary search in the following commit:

8047e09 "xen/arm: io: Use binary search for mmio handler lookup".

Signed-off-by: Bhupinder Thakur <bhupinder.thakur@linaro.org>
Signed-off-by: Stefano Stabellini <sstabellini@kernel.org>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>