Updated device name for nucleo_f746zg and disco_f746ng

Author: sarahmarshy

targets/targets.json

@@ -852,7 +852,7 @@
         "device_has": ["ANALOGIN", "ANALOGOUT", "CAN", "I2C", "I2CSLAVE", "INTERRUPTIN", "LOWPOWERTIMER", "PORTIN", "PORTINOUT", "PORTOUT", "PWMOUT", "RTC", "SERIAL", "SERIAL_ASYNCH", "SLEEP", "SPI", "SPISLAVE", "STDIO_MESSAGES", "TRNG"],
         "features": ["LWIP"],
         "release_versions": ["2", "5"],
-        "device_name": "stm32ff746zg"
+        "device_name": "STM32F746ZG"
     },
     "NUCLEO_F767ZI": {
         "inherits": ["Target"],
@@ -1073,7 +1073,7 @@
         "device_has": ["ANALOGIN", "ANALOGOUT", "CAN", "I2C", "I2CSLAVE", "INTERRUPTIN", "LOWPOWERTIMER", "PORTIN", "PORTINOUT", "PORTOUT", "PWMOUT", "RTC", "SERIAL", "SERIAL_ASYNCH", "SLEEP", "SPI", "SPISLAVE", "STDIO_MESSAGES", "TRNG"],
         "features": ["LWIP"],
         "release_versions": ["2", "5"],
-        "device_name": "stm32f746ng"
+        "device_name": "STM32F746NG"
     },
     "DISCO_F769NI": {
         "inherits": ["Target"],