USB: usbserial: fix mos7720 dependencies

Fix mos7720 Kconfig dependencies.
When an enabled bool selects a tristate, the tristate becomes =y,
even if it should be limited to modular, so limit the bool kconfig
option to configs that will build cleanly.
Also change the if-block to a simple depends on.

drivers/built-in.o: In function `mos7720_release':
mos7720.c:(.text+0xad432): undefined reference to `parport_remove_port'
drivers/built-in.o: In function `mos7715_parport_init':
mos7720.c:(.text+0xae197): undefined reference to `parport_register_port'
mos7720.c:(.text+0xae210): undefined reference to `parport_announce_port'
drivers/built-in.o:(.data+0x201c8): undefined reference to `parport_ieee1284_read_nibble'
drivers/built-in.o:(.data+0x201d0): undefined reference to `parport_ieee1284_read_byte'

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/serial/Kconfig

@@ -425,16 +425,15 @@ config USB_SERIAL_MOS7720
 	  To compile this driver as a module, choose M here: the
 	  module will be called mos7720.
 
-if USB_SERIAL_MOS7720
 config USB_SERIAL_MOS7715_PARPORT
 	bool "Support for parallel port on the Moschip 7715"
+	depends on USB_SERIAL_MOS7720
+	depends on PARPORT=y || PARPORT=USB_SERIAL_MOS7720
 	select PARPORT_NOT_PC
-	depends on PARPORT
 	---help---
 	Say Y if you have a Moschip 7715 device and would like to use
 	the parallel port it provides.  The port will register with
 	the parport subsystem as a low-level driver.
-endif
 
 config USB_SERIAL_MOS7840
 	tristate "USB Moschip 7840/7820 USB Serial Driver"