uml: Pushdown the bkl from harddog_kern ioctl

Pushdown the bkl to harddog_ioctl.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: Uml <user-mode-linux-devel@lists.sourceforge.net>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: John Kacur <jkacur@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>