Grow: Move update_tail assign to Grow_reshape()

Grow: Move update_tail assign to Grow_reshape()

Due to e919fb0af245 ("FIX: Enable metadata updates for raid0") code
can't enter super-intel.c:3415, resulting in checkpoint not being
saved to metadata for second volume in matrix raid array.
This results in checkpoint being stuck at last value for the
first volume.

Move st->update_tail to Grow_reshape() so it is assigned for each
volume.

Signed-off-by: Mateusz Kusiak <mateusz.kusiak@intel.com>
Signed-off-by: Mariusz Tkaczyk <mariusz.tkaczyk@linux.intel.com>