staging: speakup: remove NULL comparison

This was done using cocccinelle script:
@@
identifier arg;
@@

-arg==NULL
+!arg

Signed-off-by: Aastha Gupta <aastha.gupta4104@gmail.com>
Reviewed-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/speakup/main.c

@@ -2096,7 +2096,7 @@ speakup_key(struct vc_data *vc, int shift_state, int keycode, u_short keysym,
 	u_char shift_info, offset;
 	int ret = 0;
 
-	if (synth == NULL)
+	if (!synth)
 		return 0;
 
 	spin_lock_irqsave(&speakup_info.spinlock, flags);