RDMA: Use kzalloc for allocating only one thing

Use kzalloc rather than kcalloc(1,...)

The semantic patch that makes this change is as follows:
(http://coccinelle.lip6.fr/)

// <smpl>
@@
@@

- kcalloc(1,
+ kzalloc(
          ...)
// </smpl>

Link: https://lore.kernel.org/r/20201229135223.23815-1-zhengyongjun3@huawei.com
Link: https://lore.kernel.org/r/20201229135232.23869-1-zhengyongjun3@huawei.com


Signed-off-by: Zheng Yongjun <zhengyongjun3@huawei.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>