USB: OHCI: use dma_pool_zalloc

We should use new API dma_pool_zalloc instead of dma_pool_alloc/memset.

Signed-off-by: Shashi Bhusan <shashibhushan4u123@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>