BKL: Remove BKL from do_new_mount()

After pushing down the BKL to the get_sb/fill_super operations of the
filesystems that still make usage of the BKL it is safe to remove it from
do_new_mount().

I've read through all the code formerly covered by the BKL inside
do_kern_mount() and have satisfied myself that it doesn't need the BKL
any more.

Signed-off-by: Jan Blunck <jblunck@infradead.org>
Cc: Matthew Wilcox <matthew@wil.cx>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>