ASoC: mid-x86: Fix dependency on intel_sst driver

Enabling medfield asoc driver causes compliation error when intel_sst
is not selected
ERROR: "register_sst_card" [sound/soc/mid-x86/snd-soc-sst-platform.ko]
undefined!

This patch puts proper dependency to elimate build error
Signed-off-by: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Harsha Priya <priya.harsha@intel.com>
Reported-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

sound/soc/mid-x86/Kconfig

 config SND_MFLD_MACHINE
 	tristate "SOC Machine Audio driver for Intel Medfield MID platform"
 	depends on INTEL_SCU_IPC
+	depends on SND_INTEL_SST
 	select SND_SOC_SN95031
 	select SND_SST_PLATFORM
 	help
@@ -11,4 +12,3 @@ config SND_MFLD_MACHINE
 
 config SND_SST_PLATFORM
 	tristate
-	depends on SND_INTEL_SST