dmaengine: ioatdma: fix u16 overflow in cleanup

If the allocation order is 16, then the u16 count will overflow and wrap
to zero when assigned the value 1 << 16.

Change the type of 'total_descs' to int, so that it is large enough to
store a value equal or greater than 1 << 16.

Signed-off-by: Allen Hubbe <Allen.Hubbe@emc.com>
Acked-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>