[CIFS] lock inode open file list in close in case racing with open

Harmless since it only protected turning off caching for the
inode, but cleaner to lock around this in case we have a close
racing with open.

Signed-off-by: Shaggy <shaggy@us.ibm.com>
CC: Cyrill Gorcunov <gorcunov@gmail.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>