ipe: policy_fs: fix kernel-doc warnings

ipe: policy_fs: fix kernel-doc warnings

Use the "struct" keyword in kernel-doc when describing struct
ipefs_file. Add kernel-doc for the struct members also.

Don't use kernel-doc notation for 'policy_subdir'. kernel-doc does
not support documentation comments for data definitions.

This eliminates multiple kernel-doc warnings:

security/ipe/policy_fs.c:21: warning: cannot understand function prototype: 'struct ipefs_file '
security/ipe/policy_fs.c:407: warning: cannot understand function prototype: 'const struct ipefs_file policy_subdir[] = '

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Fan Wu <wufan@kernel.org>
Cc: Paul Moore <paul@paul-moore.com>
Cc: James Morris <jmorris@namei.org>
Cc: Serge E. Hallyn <serge@hallyn.com>
Cc: linux-security-module@vger.kernel.org
Signed-off-by: Fan Wu <wufan@kernel.org>