Staging: gdm724x: use match_string() helper

match_string() returns the index of an array for a matching string,
which can be used instead of open coded variant.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Quytelda Kahja <quytelda@tamalin.org>
Cc: devel@driverdev.osuosl.org
Signed-off-by: Yisheng Xie <xieyisheng1@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/gdm724x/gdm_tty.c

@@ -33,7 +33,7 @@ static struct tty_driver *gdm_driver[TTY_MAX_COUNT];
 static struct gdm *gdm_table[TTY_MAX_COUNT][GDM_TTY_MINOR];
 static DEFINE_MUTEX(gdm_table_lock);
 
-static char *DRIVER_STRING[TTY_MAX_COUNT] = {"GCTATC", "GCTDM"};
+static const char *DRIVER_STRING[TTY_MAX_COUNT] = {"GCTATC", "GCTDM"};
 static char *DEVICE_STRING[TTY_MAX_COUNT] = {"GCT-ATC", "GCT-DM"};
 
 static void gdm_port_destruct(struct tty_port *port)
@@ -55,22 +55,14 @@ static int gdm_tty_install(struct tty_driver *driver, struct tty_struct *tty)
 {
 	struct gdm *gdm = NULL;
 	int ret;
-	int i;
-	int j;
-
-	j = GDM_TTY_MINOR;
-	for (i = 0; i < TTY_MAX_COUNT; i++) {
-		if (!strcmp(tty->driver->driver_name, DRIVER_STRING[i])) {
-			j = tty->index;
-			break;
-		}
-	}
 
-	if (j == GDM_TTY_MINOR)
+	ret = match_string(DRIVER_STRING, TTY_MAX_COUNT,
+			   tty->driver->driver_name);
+	if (ret < 0)
 		return -ENODEV;
 
 	mutex_lock(&gdm_table_lock);
-	gdm = gdm_table[i][j];
+	gdm = gdm_table[ret][tty->index];
 	if (!gdm) {
 		mutex_unlock(&gdm_table_lock);
 		return -ENODEV;