ASoC: intel - atom: fix sst_platform_compr_ops declaration

Sparse complains that sst_platform_compr_ops should be static, but the
declaration of this symbol was not correct so declare the symbol as
extern in header file

sound/soc/intel/atom/sst-mfld-platform-compress.c:257:22: warning: symbol
'sst_platform_compr_ops' was not declared. Should it be static?
Signed-off-by: Vinod Koul <vinod.koul@intel.com>
Acked-by: Liam Girdwood <liam.r.girdwood@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/intel/atom/sst-mfld-platform-pcm.c

@@ -33,7 +33,6 @@
 
 struct sst_device *sst;
 static DEFINE_MUTEX(sst_lock);
-extern struct snd_compr_ops sst_platform_compr_ops;
 
 int sst_register_dsp(struct sst_device *dev)
 {

sound/soc/intel/atom/sst-mfld-platform.h

@@ -25,6 +25,7 @@
 #include "sst-atom-controls.h"
 
 extern struct sst_device *sst;
+extern struct snd_compr_ops sst_platform_compr_ops;
 
 #define SST_MONO		1
 #define SST_STEREO		2