coccinelle: add patch rule for dma_alloc_coherent

Commit dfd32cad ("dma-mapping: remove dma_zalloc_coherent()")
removed the definition of dma_zalloc_coherent() and also removed the
corresponding patch rule for replacing instances of dma_alloc_coherent +
memset in zalloc-simple.cocci (though left the report rule).

Add a new patch rule to remove unnecessary calls to memset after
allocating with dma_alloc_coherent. While we're at it, fix a couple of
typos.

Fixes: dfd32cad ("dma-mapping: remove dma_zalloc_coherent()")
Signed-off-by: Alex Dewar <alex.dewar90@gmail.com>
Signed-off-by: Julia Lawall <Julia.Lawall@inria.fr>