Add configuration of LF clk source in targer.json for targets MCU_NRF51 & MCU_NRF52

Fix typo

Author: nvlsianpu

hal/targets.json

@@ -1107,7 +1107,13 @@
         },
         "program_cycle_s": 6,
         "default_build": "small",
-        "features": ["BLE"]
+        "features": ["BLE"],
+        "config":{
+            "lf_clock_src": {
+                "value": "NRF_LF_SRC_XTAL",
+                "macro_name": "MBED_CONF_NORDIC_NRF_LF_CLOCK_SRC"
+            }
+        }
     },
     "MCU_NRF51_16K_BASE": {
         "inherits": ["MCU_NRF51"],
@@ -1721,7 +1727,13 @@
             "toolchains": ["ARM_STD", "GCC_ARM"]
         },
         "MERGE_BOOTLOADER": false,
-        "features": ["BLE"]
+        "features": ["BLE"],
+        "config":{
+            "lf_clock_src": {
+                "value": "NRF_LF_SRC_XTAL",
+                "macro_name": "MBED_CONF_NORDIC_NRF_LF_CLOCK_SRC"
+            }
+        }
     },
     "NRF52_DK": {
         "supported_form_factors": ["ARDUINO"],

hal/targets/cmsis/TARGET_NORDIC/TARGET_NRF5/nrf5x_lf_clk_helper.h

@@ -38,9 +38,9 @@
 
 #ifndef __NRF5X_LF_CLK_HELPER_H_
 
-#ifndef MBED_CONF_APP_NORDIC_NRF_LF_CLOCK_SRC
-    #define MBED_CONF_APP_NORDIC_NRF_LF_CLOCK_SRC (NRF_LF_SRC_XTAL)
-    #warning Non of LF clk src configurartion! Sett to LF Xtal.
+#ifndef MBED_CONF_NORDIC_NRF_LF_CLOCK_SRC
+    #define MBED_CONF_NORDIC_NRF_LF_CLOCK_SRC (NRF_LF_SRC_XTAL)
+    #warning No configuration for LF clock source. Xtal source will be used as a default configuration.
 #endif
 
 
@@ -49,11 +49,11 @@
 #define NRF_LF_SRC_SYNTH 3 
 #define NRF_LF_SRC_RC    4
 
-#if MBED_CONF_APP_NORDIC_NRF_LF_CLOCK_SRC == NRF_LF_SRC_SYNTH
+#if MBED_CONF_NORDIC_NRF_LF_CLOCK_SRC == NRF_LF_SRC_SYNTH
     #define CLOCK_LFCLKSRC_SRC_TO_USE (CLOCK_LFCLKSRC_SRC_Synth)
-#elif MBED_CONF_APP_NORDIC_NRF_LF_CLOCK_SRC == NRF_LF_SRC_XTAL
+#elif MBED_CONF_NORDIC_NRF_LF_CLOCK_SRC == NRF_LF_SRC_XTAL
     #define CLOCK_LFCLKSRC_SRC_TO_USE (CLOCK_LFCLKSRC_SRC_Xtal)
-#elif MBED_CONF_APP_NORDIC_NRF_LF_CLOCK_SRC == NRF_LF_SRC_RC
+#elif MBED_CONF_NORDIC_NRF_LF_CLOCK_SRC == NRF_LF_SRC_RC
     #define CLOCK_LFCLKSRC_SRC_TO_USE (CLOCK_LFCLKSRC_SRC_RC)
 #else
     #error Bad LFCLK configuration. Declare proper source through mbed configuration.