[alsa-devel] pcm: Add missing callbacks that cannot be NULL

Some plugins don't implement some mandatory fast_ops. Thus, these fast_ops get defaulted to NULL, and programs crash when calling the corresponding snd_pcm_* functions.

The following callbacks were missing:

file: htimestamp multi: rewindable, forwardable null: rewindable, forwardable rate: rewindable, forwardable

After this series, all required callbacks are present, but I cannot guarantee that they return meaningful values.

All patches in this series are only compile-tested.