USB-BKL: Remove lock_kernel in usbfs update_sb()

The code this is attempting to lock against does not use the BKL,
so it's not needed.

Most likely this code is still broken/racy (Al Viro also thinks so),
but removing the BKL should not make it worse than before.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>