ecryptfs: mmap: Help out one function header and demote other abuses

ecryptfs: mmap: Help out one function header and demote other abuses

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

 fs/ecryptfs/mmap.c:26: warning: Incorrect use of kernel-doc format:  * ecryptfs_get_locked_page
 fs/ecryptfs/mmap.c:34: warning: Function parameter or member 'inode' not described in 'ecryptfs_get_locked_page'
 fs/ecryptfs/mmap.c:34: warning: Function parameter or member 'index' not described in 'ecryptfs_get_locked_page'
 fs/ecryptfs/mmap.c:34: warning: expecting prototype for eCryptfs(). Prototype was for ecryptfs_get_locked_page() instead
 fs/ecryptfs/mmap.c:52: warning: Function parameter or member 'wbc' not described in 'ecryptfs_writepage'
 fs/ecryptfs/mmap.c:98: warning: Incorrect use of kernel-doc format:  * ecryptfs_copy_up_encrypted_with_header
 fs/ecryptfs/mmap.c:110: warning: Function parameter or member 'page' not described in 'ecryptfs_copy_up_encrypted_with_header'
 fs/ecryptfs/mmap.c:110: warning: Function parameter or member 'crypt_stat' not described in 'ecryptfs_copy_up_encrypted_with_header'
 fs/ecryptfs/mmap.c:110: warning: expecting prototype for Header Extent(). Prototype was for ecryptfs_copy_up_encrypted_with_header() instead
 fs/ecryptfs/mmap.c:233: warning: wrong kernel-doc identifier on line:
 fs/ecryptfs/mmap.c:379: warning: Function parameter or member 'ecryptfs_inode' not described in 'ecryptfs_write_inode_size_to_header'

Cc: Tyler Hicks <code@tyhicks.com>
Cc: James Morris <jamorris@linux.microsoft.com>
Cc: Tycho Andersen <tycho@tycho.pizza>
Cc: Christian Brauner <christian.brauner@ubuntu.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>