ALSA: timer: Don't take register_mutex with copy_from/to_user()

In the Linux kernel, the following vulnerability has been resolved:

ALSA: timer: Don't take register_mutex with copy_from/to_user()

The infamous mmap_lock taken in copy_from/to_user() can be often

problematic when it's called inside another mutex, as they might lead

to deadlocks.

In the case of ALSA timer code, the bad pattern is with

guard(mutex)(&register_mutex) that covers copy_from/to_user() -- which

was mistakenly introduced at converting to guard(), and it had been

carefully worked around in the past.

This patch fixes those pieces simply by moving copy_from/to_user() out

of the register mutex lock again.