Bluetooth: PACS: Set PACS read_buf size to BT_ATT_MAX_ATTRIBUTE_LEN

The maximum size of the characteristic is BT_ATT_MAX_ATTRIBUTE_LEN.
The previous size limited the size of the characteristic to
the maximum possible MTU, thus not utlizing support for the
Read Long procedure.

Signed-off-by: Emil Gydesen <emil.gydesen@nordicsemi.no>
diff --git a/subsys/bluetooth/audio/pacs.c b/subsys/bluetooth/audio/pacs.c
index 982895b..ce8144d1 100644
--- a/subsys/bluetooth/audio/pacs.c
+++ b/subsys/bluetooth/audio/pacs.c
@@ -73,7 +73,7 @@
 #endif /* CONFIG_BT_PAC_SRC */
 
 static K_SEM_DEFINE(read_buf_sem, 1, 1);
-NET_BUF_SIMPLE_DEFINE_STATIC(read_buf, CONFIG_BT_L2CAP_TX_MTU);
+NET_BUF_SIMPLE_DEFINE_STATIC(read_buf, BT_ATT_MAX_ATTRIBUTE_LEN);
 
 static ssize_t pac_data_add(struct net_buf_simple *buf, size_t count,
 			    struct bt_codec_data *data)