check-alsabat.sh: use 821Hz as default test frequency

Lower the default test frequency from 997Hz to 821Hz. Most SOF
topologies use 1000Hz tick rate, and test frequency close to this
scheduling frequency can mask certain type of errors (like SOF bug

Link: thesofproject/sof#6709
Suggested-by: Seppo Ingalsuo <seppo.ingalsuo@linux.intel.com>
Signed-off-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>

Author: kv2019i

test-case/check-alsabat.sh

@@ -34,7 +34,7 @@ OPT_NAME['c']='pcm_c'      	OPT_DESC['c']='pcm for capture. Example: hw:1,0'
 OPT_HAS_ARG['c']=1             OPT_VAL['c']=''
 
 OPT_NAME['f']='frequency'       OPT_DESC['f']='target frequency'
-OPT_HAS_ARG['f']=1             OPT_VAL['f']=997
+OPT_HAS_ARG['f']=1             OPT_VAL['f']=821
 
 OPT_NAME['n']='frames'          OPT_DESC['n']='test frames'
 OPT_HAS_ARG['n']=1             OPT_VAL['n']=240000