tty: n_gsm: Fix bogus i++ in gsm_data_kick

When submitting the previous fix "tty: n_gsm: Fix waking up upper tty
layer when room available". It was suggested to switch from a while to
a for loop, but when doing it, there was a remaining bogus i++.

This patch removes this i++ and also reorganizes the code making it more
compact.

Fixes: e1eaea4 ("tty: n_gsm line discipline")
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>
Link: https://lore.kernel.org/r/20200518084517.2173242-3-gregory.clement@bootlin.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: gclement

drivers/tty/n_gsm.c

@@ -700,17 +700,9 @@ static void gsm_data_kick(struct gsm_mux *gsm, struct gsm_dlci *dlci)
 		} else {
 			int i = 0;
 
-			for (i = 0; i < NUM_DLCI; i++) {
-				struct gsm_dlci *dlci;
-
-				dlci = gsm->dlci[i];
-				if (dlci == NULL) {
-					i++;
-					continue;
-				}
-
-				tty_port_tty_wakeup(&dlci->port);
-			}
+			for (i = 0; i < NUM_DLCI; i++)
+				if (gsm->dlci[i])
+					tty_port_tty_wakeup(&gsm->dlci[i]->port);
 		}
 	}
 }