MT#61856 media_player: make `*.db_id`s unsigned

Make both `media_player_opts_t.db_id` and `media_player_content_index.db_id`
unsigned because:
- they aren't used with any guards/init values
- most DB-media API functionality actually uses `unsigned long long`

So this makes the ids consistent with the usage of them
in the actual code.

Change-Id: I6c756c537b3c992099a6857683078c169d5e030d

include/media_player.h

@@ -27,7 +27,7 @@ typedef struct {
 	unsigned int block_egress:1,
 				moh:1;
 	str file, blob;
-	long long db_id;
+	unsigned long long db_id;
 } media_player_opts_t;
 
 
@@ -41,7 +41,7 @@ struct media_player_media_file;
 
 struct media_player_content_index {
 	enum { MP_OTHER = 0, MP_FILE = 1, MP_DB, MP_BLOB } type;
-	long long db_id;
+	unsigned long long db_id;
 	str file; // file name or binary blob
 };