RDMA/rtrs-clt: Consolidate rtrs_clt_destroy_sysfs_root_{folder,files}

Since the two functions are called together, let's consolidate them in
a new function rtrs_clt_destroy_sysfs_root.

Link: https://lore.kernel.org/r/20201217141915.56989-9-jinpu.wang@cloud.ionos.com


Signed-off-by: Guoqing Jiang <guoqing.jiang@cloud.ionos.com>
Signed-off-by: Jack Wang <jinpu.wang@cloud.ionos.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>