cifs: remove "cifs_" prefix from init/destroy mids functions

Rename generic mid functions to same style, i.e. without "cifs_"
prefix.

cifs_{init,destroy}_mids() -> {init,destroy}_mids()

Signed-off-by: Enzo Matsumiya <ematsumiya@suse.de>
Signed-off-by: Steve French <stfrench@microsoft.com>