sound: oss: Use setup_timer and mod_timer.

The function setup_timer combines the initialization of a timer with the
initialization of the timer's function and data fields. The mulitiline
code for timer initialization is now replaced with function setup_timer.

Also, quoting the mod_timer() function comment:
-> mod_timer() is a more efficient way to update the expire field of an
   active timer (if the timer is inactive it will be activated).

Use setup_timer() and mod_timer() to setup and arm a timer, making the
code compact and aid readablity.

Signed-off-by: Muhammad Falak R Wani <falakreyaz@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>