toaster: use // operator instead of /

toaster: use // operator instead of /

Division operator works differently in Python 3. It results in
float unlike in Python 2, where it results in int.

Explicitly used "floor division" operator instead of 'division'
operator. This should make the code to result in integer under
both pythons.

Signed-off-by: Ed Bartosh <ed.bartosh@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>