RDMA/cma: Eliminate unnecessary remove_list

Eliminate remove_list by using list_del_init() instead during device
removal handling.

Signed-off-by: Krishna Kumar <krkumar2@in.ibm.com>
Signed-off-by: Sean Hefty <sean.hefty@intel.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>