uml: Convert to unlocked_ioctls to remove implicit BKL

Convert hostaudio_ioctl and hostmixer_ioctl_mixdev to
unlocked_ioctl without pushdown.

There is nothing to protect inside, the synchronization
is made from the host already.

Signed-off-by: John Kacur <jkacur@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Jeff Dike <jdike@addtoit.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>