ALSA: emu8000: Use swap macro in snd_emu8000_sample_new

Make use of the swap macro and remove unnecessary variable *tmp*. This
makes the code easier to read and maintain.

This code was detected with the help of Coccinelle.

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>