[media] b2c2: flexcop: avoid unused function warnings

The flexcop driver has two functions that are normally used, except
when multiple frontend drivers are disabled:

drivers/media/common/b2c2/flexcop-fe-tuner.c:42:12: warning: 'flexcop_set_voltage' defined but not used [-Wunused-function]
drivers/media/common/b2c2/flexcop-fe-tuner.c:71:12: warning: 'flexcop_sleep' defined but not used [-Wunused-function]

This avoids the build warning by updating the #ifdef for flexcop_set_voltage
to the exact condition under which it is used. For flexcop_sleep, the
condition is rather complex, so I resort to marking it as __maybe_unused,
so the compiler can silently drop it.

Signed-off-by: Arnd Bergmann <[e-mail]>
Signed-off-by: Mauro Carvalho Chehab <[e-mail]>

drivers/media/common/b2c2/flexcop-fe-tuner.c

···
 #endif
 
 /* lnb control */
-#if FE_SUPPORTED(MT312) || FE_SUPPORTED(STV0299)
+#if (FE_SUPPORTED(MT312) || FE_SUPPORTED(STV0299)) && FE_SUPPORTED(PLL)
 static int flexcop_set_voltage(struct dvb_frontend *fe,
 			       enum fe_sec_voltage voltage)
 {
···
 #endif
 
 #if FE_SUPPORTED(S5H1420) || FE_SUPPORTED(STV0299) || FE_SUPPORTED(MT312)
-static int flexcop_sleep(struct dvb_frontend* fe)
+static int __maybe_unused flexcop_sleep(struct dvb_frontend* fe)
 {
 	struct flexcop_device *fc = fe->dvb->priv;
 	if (fc->fe_sleep)