iget: stop PROCFS from using iget() and read_inode()

Stop the PROCFS filesystem from using iget() and read_inode().  Merge
procfs_read_inode() into procfs_get_inode(), and have that call iget_locked()
instead of iget().

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: David Howells <dhowells@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Acked-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>