mtd: part: Remove partition overlap checks

This patch makes MTD dynamic partitioning more flexible by removing
overlap checks for dynamic partitions. I don't see any  particular
reason why overlapping dynamic partitions should be prohibited while
static partitions are allowed to overlap freely.

The checks previously had an off-by-one error, where 'end' should be
one less than what it is currently set at, and adding partitions out of
increasing order will fail. Disabling the checks resolves this issue.

Signed-off-by: Dan Ehrenberg <dehrenberg@chromium.org>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>