RDMA/core: Print the function name by __func__ instead of an fixed string

It's better to use __func__ than a fixed string to print a function's
name.

Link: https://lore.kernel.org/r/1617783353-48249-2-git-send-email-liweihang@huawei.com


Signed-off-by: Wenpeng Liang <liangwenpeng@huawei.com>
Signed-off-by: Weihang Li <liweihang@huawei.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>