media: stb6100: mark a currently unused function as such

The stb6100_normalise_regs() function is not used with current
boards, but the driver says that some devices could need it.
Ok, we could simply drop it, but as there's a macro to mark
unused functions, use it.

This should shut up a clang warning.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

drivers/media/dvb-frontends/stb6100.c

@@ -110,7 +110,7 @@ static const struct stb6100_regmask stb6100_template[] = {
 /*
  * Currently unused. Some boards might need it in the future
  */
-static inline void stb6100_normalise_regs(u8 regs[])
+static __always_unused inline void stb6100_normalise_regs(u8 regs[])
 {
 	int i;