ASoC: Intel: Skylake: Fix NULL Pointer exception in dynamic_debug.

The following bug was reported by sometime back:

https://lkml.org/lkml/2016/6/29/795

This commit fixes this bug by setting value for the prefix string.
Signed-off-by: Vedang Patel <vedang.patel@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/intel/skylake/skl-sst-ipc.c

@@ -692,7 +692,7 @@ int skl_ipc_init_instance(struct sst_generic_ipc *ipc,
 	 /* param_block_size must be in dwords */
 	u16 param_block_size = msg->param_data_size / sizeof(u32);
 
-	print_hex_dump_debug(NULL, DUMP_PREFIX_NONE,
+	print_hex_dump_debug("Param data:", DUMP_PREFIX_NONE,
 		16, 4, buffer, param_block_size, false);
 
 	header.primary = IPC_MSG_TARGET(IPC_MOD_MSG);