cplay: remove set but not used warnings

cplay: remove set but not used warnings

cplay.c: In function ‘find_adif_header’:
cplay.c:367:13: warning: variable ‘object_type’ set but not used [-Wunused-but-set-variable]
  367 |         int object_type;
      |             ^~~~~~~~~~~

cplay.c:366:13: warning: variable ‘bitrate’ set but not used [-Wunused-but-set-variable]
  366 |         int bitrate;
      |             ^~~~~~~

cplay.c:91:27: warning: ‘DEFAULT_CODEC_ID’ defined but not used [-Wunused-const-variable=]
   91 | static const unsigned int DEFAULT_CODEC_ID = SND_AUDIOCODEC_PCM;
      |                           ^~~~~~~~~~~~~~~~

While at it, cleanup the code a bit as well removing now redundant
braces around if-else

So remove these unused variables

Signed-off-by: Vinod Koul <vkoul@kernel.org>