IB: Remove unneeded memset

In commit af7ddd8a62 ("Merge tag 'dma-mapping-4.21' of
git://git.infradead.org/users/hch/dma-mapping"),
dma_alloc_coherent/dmam_alloc_coherent always zeroed the returned memory.
So the memset after a coherent allocation function is not needed.

Signed-off-by: Fuqian Huang <huangfq.daxian@gmail.com>
Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/hw/mthca/mthca_allocator.c

@@ -214,8 +214,6 @@ int mthca_buf_alloc(struct mthca_dev *dev, int size, int max_direct,
 
 		dma_unmap_addr_set(&buf->direct, mapping, t);
 
-		memset(buf->direct.buf, 0, size);
-
 		while (t & ((1 << shift) - 1)) {
 			--shift;
 			npages *= 2;