Revert "mtd: make mtd_partition.name const"

This reverts 'commit 26a6d240 ("mtd: make
mtd_partition.name const")'. This is needed to fix the
compilation issue with msm_qpic_nand driver which makes
changes to mtd partition name.

Change-Id: Ic10df9c29d08d3df5df351f33e84a2c8e5158b43
Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>