usb: typec: fusb302: Fix an undefined reference to 'extcon_get_state'

Fixes the following compile error:

drivers/usb/typec/tcpm/fusb302.o: In function `tcpm_get_current_limit':
fusb302.c:(.text+0x3ee): undefined reference to `extcon_get_state'
fusb302.c:(.text+0x422): undefined reference to `extcon_get_state'
fusb302.c:(.text+0x450): undefined reference to `extcon_get_state'
fusb302.c:(.text+0x48c): undefined reference to `extcon_get_state'
drivers/usb/typec/tcpm/fusb302.o: In function `fusb302_probe':
fusb302.c:(.text+0x980): undefined reference to `extcon_get_extcon_dev'
make: *** [vmlinux] Error 1

It is because EXTCON is build as a module, but FUSB302 is not.
Suggested-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: zhong jiang <zhongjiang@huawei.com>
Acked-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/1576239378-50795-1-git-send-email-zhongjiang@huawei.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/typec/tcpm/Kconfig

@@ -32,6 +32,7 @@ endif # TYPEC_TCPCI
 config TYPEC_FUSB302
 	tristate "Fairchild FUSB302 Type-C chip driver"
 	depends on I2C
+	depends on EXTCON || !EXTCON
 	help
 	  The Fairchild FUSB302 Type-C chip driver that works with
 	  Type-C Port Controller Manager to provide USB PD and USB