Fix NPE in updateAddPreference

Update mAddFingerprintPreference to avoid NPE

Fixes: 286495189
Test: Rotate screen during first fingerprint enrollment, complete enrollment, and observe no crash
Change-Id: Id7edde492168b467360c6c99b326721cd883bba8
Merged-In: Id7edde492168b467360c6c99b326721cd883bba8

src/com/android/settings/biometrics/fingerprint/FingerprintSettings.java

@@ -623,9 +623,9 @@ public class FingerprintSettings extends SubSettings {
                 return; // Activity went away
             }
 
-            final Preference addPreference = findPreference(KEY_FINGERPRINT_ADD);
+            mAddFingerprintPreference = findPreference(KEY_FINGERPRINT_ADD);
 
-            if (addPreference == null) {
+            if (mAddFingerprintPreference == null) {
                 return; // b/275519315 Skip if updateAddPreference() invoke before addPreference()
             }