Set correct reshape restart position

Set correct reshape restart position

This patch version is simplified compared to previous one.
There is no use of freeze_reshape flag in start_reshape(). It is assumed
that for reshape starting condition reshape_progress field contains
0 value /correct start position/. For reshape restart case, it contains
correct restart position. This approach doesn't make start_reshape()
difficult to read/manage and /imho/ kernel changes to change mdstat
reporting behavior are not necessary.

Setting correct position allows user to see it in the mdstat during
reshape restart and reshape process is not reported as resync.

Signed-off-by: Adam Kwolek <adam.kwolek@intel.com>
Signed-off-by: NeilBrown <neilb@suse.de>