ASoC: SOF: ipc-msg-injector: Fix reversed if statement

This if statement is reversed.  In fact, the condition can just be
deleted because writing zero bytes is a no-op.

Fixes: 066c6762 ("ASoC: SOF: ipc-msg-injector: Add support for IPC4 messages")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Peter Ujfalusi <peter.ujfalusi@linux.intel.com>
Link: https://lore.kernel.org/r/Yph+T3PpGCdPsEDj@kiliSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/sof/sof-client-ipc-msg-injector.c

@@ -200,7 +200,6 @@ static ssize_t sof_msg_inject_ipc4_dfs_write(struct file *file,
 		return -EFAULT;
 
 	count -= size;
-	if (!count) {
 	/* Copy the payload */
 	size = simple_write_to_buffer(ipc4_msg->data_ptr,
 				      priv->max_msg_size, ppos, buffer,
@@ -209,7 +208,6 @@ static ssize_t sof_msg_inject_ipc4_dfs_write(struct file *file,
 		return size;
 	if (size != count)
 		return -EFAULT;
-	}
 
 	ipc4_msg->data_size = count;