ramfs: support O_TMPFILE

[akpm@linux-foundation.org: update inode_operations.tmpfile]

Link: http://lkml.kernel.org/r/20190206073349.GA15311@avx2


Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>