BootReceiver: changed deprecated Build.RADIO to Build.getRadioVerison to get non-empty radio firmware version in SYSTEM_LAST_KMSG.

Test: Manually verified on Pixel 2 XL, Nexus 5X and 6P devices.
BUG:70934228
Change-Id: I40da7e659619e06587409c6b83c655b46bcbd5b2

core/java/com/android/server/BootReceiver.java

@@ -161,7 +161,7 @@ public class BootReceiver extends BroadcastReceiver {
             .append("Revision: ")
             .append(SystemProperties.get("ro.revision", "")).append("\n")
             .append("Bootloader: ").append(Build.BOOTLOADER).append("\n")
-            .append("Radio: ").append(Build.RADIO).append("\n")
+            .append("Radio: ").append(Build.getRadioVersion()).append("\n")
             .append("Kernel: ")
             .append(FileUtils.readTextFile(new File("/proc/version"), 1024, "...\n"))
             .append("\n").toString();