cifs: don't pass superblock to cifs_mount()

cifs: don't pass superblock to cifs_mount()

To close sget() races we'll need to be able to set cifs_sb up before
we get the superblock, so we'll want to be able to do cifs_mount()
earlier.  Fortunately, it's easy to do - setting ->s_maxbytes can
be done in cifs_read_super(), ditto for ->s_time_gran and as for
putting MS_POSIXACL into ->s_flags, we can mirror it in ->mnt_cifs_flags
until cifs_read_super() is called.  Kill unused 'devname' argument,
while we are at it...

Acked-by: Pavel Shilovsky <[email protected]>
Reviewed-by: Jeff Layton <[email protected]>
Signed-off-by: Al Viro <[email protected]>