[media] stv090x: remove export symbol for stv090x_set_gpio()

Drivers that use dvb_attach can have just one exported symbol,
or they will cause compilation breakages depending on the
selected frontends.

As Jim reported:
drivers/built-in.o: In function `technisat_usb2_set_voltage':
technisat-usb2.c:(.text+0x3b4919): undefined reference to `stv090x_set_gpio'
make: *** [vmlinux] Error 1

That happens because, on his configuration, the configuration
is:

	CONFIG_DVB_USB=y
	CONFIG_DVB_STV090x=m

Luis proposed ar way to fix, but that would just force the
STV090x to be selected, even if one wants to use a device
with a different frontend.

Instead, let's do the right thing: move set_gpio to the
configuration structure and fill it during dvb_attach().

This way, the driver can still call it, and dvb_attach()
will load stv090x module only if the device really needs it.

Reported by: Jim Davis <jim.epost@gmail.com>

Cc: Luis Rodriguez <mcgrof@suse.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

drivers/media/usb/dvb-usb/technisat-usb2.c

@@ -449,6 +449,8 @@ static int technisat_usb2_read_mac_address(struct dvb_usb_device *d,
 	return 0;
 }
 
+static struct stv090x_config technisat_usb2_stv090x_config;
+
 /* frontend attach */
 static int technisat_usb2_set_voltage(struct dvb_frontend *fe,
 		fe_sec_voltage_t voltage)
@@ -472,7 +474,8 @@ static int technisat_usb2_set_voltage(struct dvb_frontend *fe,
 	}
 
 	for (i = 0; i < 3; i++)
-		if (stv090x_set_gpio(fe, i+2, 0, gpio[i], 0) != 0)
+		if (technisat_usb2_stv090x_config.set_gpio(fe, i+2, 0,
+							   gpio[i], 0) != 0)
 			return -EREMOTEIO;
 	return 0;
 }