hal: Assign correct FM port for SDM670

Loopback gain setting failed in DSP due to invalid FM
port configuration. Assign correct FM backend port
to fix this issue.

CRs-Fixed: 2127308
Change-Id: Iaf8106f1dda40e84e8128331f1e3c0cc4556ea62
diff --git a/hal/msm8974/platform.h b/hal/msm8974/platform.h
index 387ef25..4fa9442 100644
--- a/hal/msm8974/platform.h
+++ b/hal/msm8974/platform.h
@@ -491,7 +491,7 @@
 #define FM_RX_VOLUME "PRI MI2S LOOPBACK Volume"
 #elif PLATFORM_MSM8996
 #define FM_RX_VOLUME "Tert MI2S LOOPBACK Volume"
-#elif defined (PLATFORM_MSM8998) || defined (PLATFORM_SDM845) || defined (PLATFORM_MSMFALCON)
+#elif defined (PLATFORM_MSM8998) || defined (PLATFORM_SDM845) || defined (PLATFORM_MSMFALCON) || defined (PLATFORM_SDM670)
 #define FM_RX_VOLUME "SLIMBUS_8 LOOPBACK Volume"
 #else
 #define FM_RX_VOLUME "Internal FM RX Volume"