DaVinci: EDMA: Fix bug in edma_free_cont_slots API

In the edma_free_cont_slots API, the variable slot was being modified
and then used in the for loop.
This results in incorrect behaviour when the API is used.

Signed-off-by: Sandeep Paulraj <s-paulraj@ti.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>