ecryptfs: file: Demote kernel-doc abuses

Fixes the following W=1 kernel build warning(s):

 fs/ecryptfs/file.c:23: warning: Incorrect use of kernel-doc format:  * ecryptfs_read_update_atime
 fs/ecryptfs/file.c:34: warning: Function parameter or member 'iocb' not described in 'ecryptfs_read_update_atime'
 fs/ecryptfs/file.c:34: warning: Function parameter or member 'to' not described in 'ecryptfs_read_update_atime'
 fs/ecryptfs/file.c:34: warning: expecting prototype for eCryptfs(). Prototype was for ecryptfs_read_update_atime() instead

Cc: Tyler Hicks <code@tyhicks.com>
Cc: "Michael A. Halcrow" <mhalcrow@us.ibm.com>
Cc: "Michael C. Thompson" <mcthomps@us.ibm.com>
Cc: ecryptfs@vger.kernel.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Tyler Hicks <code@tyhicks.com>