[ALSA] Remove redundant NULL checks before kfree

Timer Midlevel,ALSA sequencer,ALSA<-OSS sequencer,Digigram VX core
I2C tea6330t,GUS Library,VIA82xx driver,VIA82xx-modem driver
CA0106 driver,CS46xx driver,EMU10K1/EMU10K2 driver,YMFPCI driver
Digigram VX Pocket driver,Common EMU synth,USB generic driver,USB USX2Y
Checking a pointer for NULL before calling kfree() on it is redundant,
kfree() deals with NULL pointers just fine.
This patch removes such checks from sound/

This patch also makes another, but closely related, change.
It avoids casting pointers about to be kfree()'ed.

Signed-off-by: Jesper Juhl <juhl-lkml@dif.dk>
Signed-off-by: Takashi Iwai <tiwai@suse.de>