staging: gdm724x: depend on CONFIG_TTY

The driver uses the tty layer, so explicitly say that, to prevent
randomconfig build errors.
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/gdm724x/Kconfig

@@ -4,7 +4,7 @@
 
 config LTE_GDM724X
 	tristate "GCT GDM724x LTE support"
-	depends on NET && USB && m
+	depends on NET && USB && TTY && m
 	help
 	  This driver supports GCT GDM724x LTE chip based USB modem devices.
 	  It exposes 4 network devices to be used per PDN and 2 tty devices to be