topology: fix unused-variable warnings introduced to build_link()

topology: fix unused-variable warnings introduced to build_link()

A function with unused automatic variables was recently introduced to this
library, then compiler generates below warnings.

pcm.c: In function ‘build_link’:
pcm.c:213:6: warning: unused variable ‘i’ [-Wunused-variable]
  int i, num_hw_configs = 0, err = 0;
      ^
pcm.c:210:43: warning: unused variable ‘cmpnt’ [-Wunused-variable]
  struct snd_soc_tplg_link_cmpnt  *codec, *cmpnt;
                                           ^~~~~
pcm.c:210:35: warning: unused variable ‘codec’ [-Wunused-variable]
  struct snd_soc_tplg_link_cmpnt  *codec, *cmpnt;
                                   ^~~~~
pcm.c:209:20: warning: unused variable ‘ref_elem’ [-Wunused-variable]
  struct tplg_elem *ref_elem = NULL;

This commit removes them.

Fixes: 53f7711769d4("topology: Define a function to build a single physical DAI link")
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>