tinycompress: cplay: make functions static

tinycompress: cplay: make functions static

Sparse rightly complains some functions should be static so make them static

cplay.c:100:5: warning: symbol 'parse_mp3_header' was not declared. Should it be static?
cplay.c:129:5: warning: symbol 'check_codec_format_supported' was not declared. Should it be static?
../../include/tinycompress/tinymp3.h:66:11: warning: symbol 'mp3_sample_rates' was not declared. Should it be static?
../../include/tinycompress/tinymp3.h:72:11: warning: symbol 'mp3_bit_rates' was not declared. Should it be static?

Signed-off-by: Vinod Koul <vinod.koul@intel.com>