ramfs: fix mount source show for ramfs

ramfs: fix mount source show for ramfs

ramfs_parse_param does not parse the key "source", and will convert
-ENOPARAM to 0.  This will skip calling vfs_parse_fs_param_source() in
vfs_parse_fs_param(), which leads to always presenting "none" as the mount
source for ramfs.  Fix it by parsing "source" in ramfs_parse_param().

Link: https://lkml.kernel.org/r/20210811122811.2288041-1-yangerkun@huawei.com
Signed-off-by: yangerkun <yangerkun@huawei.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Yu Kuai <yukuai3@huawei.com>
Cc: ErKun Yang <yangerkun@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>