ALSA: timer: Unify master/slave linking code

The code in both snd_timer_check_master() and snd_timer_check_slave()
are almost identical, both check whether the master/slave link and
does linkage.  Factor out the common code and call it from both
functions for readability.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Link: https://lore.kernel.org/r/20191107192008.32331-2-tiwai@suse.de


Signed-off-by: Takashi Iwai <tiwai@suse.de>