ivshmem: fix overlap detection

ivshmem: fix overlap detection

Partial revert of an earlier ill-conceived "fix".
Adjacent segments can never be considered overlapping because we
are not comparing ends to starts, but rather starts to starts.
Therefore the earlier fix was wrong (plus it also had a typo).

Fixes: d6cf31419e51 ("ivshmem: avoid infinite loop when concatenating segments")

Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>
Tested-by: Ferruh Yigit <ferruh.yigit@intel.com>
Acked-by: Ferruh Yigit <ferruh.yigit@intel.com>