[ALSA] at73c213: fix error checking for clk API

The clk_round_rate() and clk_set_rate() will return int, so not store thier
return value to unsigned long variable.  This bug hides real error on these
API.

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>