RDMA/uverbs: fix ptr_ret.cocci warnings

drivers/infiniband/core/uverbs_cmd.c:1095:1-3: WARNING: PTR_ERR_OR_ZERO can be used

 Use PTR_ERR_OR_ZERO rather than if(IS_ERR(...)) + PTR_ERR

Generated by: scripts/coccinelle/api/ptr_ret.cocci

Fixes: 7106a976

 ("RDMA/uverbs: Make write() handlers return 0 on success")
Signed-off-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>