Add a size argument to rs_set_dev_and_array_sectors as prerequisite
to fixing grown device resynchronization not occuring when new MD
bitmap pages have to be allocated as a result of the extension in
a follwup patch.

Also avoid code duplication by using rs_set_rdev_sectors
in the aforementioned function.
Signed-off-by: NHeinz Mauelshagen <heinzm@redhat.com>
Signed-off-by: NMike Snitzer <snitzer@redhat.com>