Fix warning for uninitialized variable.

Change-Id: I78e6a20562419dcc2fb3f579089b32aeb5538f8b
diff --git a/fastbootd/commands/partitions.c b/fastbootd/commands/partitions.c
index 74232e6..f2c9da7 100644
--- a/fastbootd/commands/partitions.c
+++ b/fastbootd/commands/partitions.c
@@ -547,7 +547,8 @@
 int GPT_parse_entry(char *string, struct GPT_entry_raw *entry)
 {
     char *ptr = string;
-    char *key, *value;
+    char *key = NULL;
+    char *value = NULL;
 
     while ((ptr = get_key_value(ptr, &key, &value)) != NULL) {
         if (add_key_value(key, value, entry)) {