kernel: drop unneeded modification of mtd_add_partition function

kernel: drop unneeded modification of mtd_add_partition function

In old days mtd_add_partition was checking for partitions overlapping
which was breaking our splitting feature. We had to modify this function
by adding an extra bool dup_check parameter. Upstream commit:
3a434f66e6da ("mtd: part: Remove partition overlap checks")
removed that check so we don't need our modification anymore.

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
SVN-Revision: 47748