ecryptfs: dentry: File headers are not good candidates for kernel-doc

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

 fs/ecryptfs/dentry.c:19: warning: Incorrect use of kernel-doc format:  * ecryptfs_d_revalidate - revalidate an ecryptfs dentry
 fs/ecryptfs/dentry.c:32: warning: Function parameter or member 'dentry' not described in 'ecryptfs_d_revalidate'
 fs/ecryptfs/dentry.c:32: warning: Function parameter or member 'flags' not described in 'ecryptfs_d_revalidate'
 fs/ecryptfs/dentry.c:32: warning: expecting prototype for eCryptfs(). Prototype was for ecryptfs_d_revalidate() instead

Cc: Tyler Hicks <code@tyhicks.com>
Cc: "Michael A. Halcrow" <mahalcro@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>