media: dvb: mb86a20s: get rid of a clang-15 warning

When building with clang-15: this warning is produced:

	../drivers/media/dvb-frontends/mb86a20s.c:1572:6: error: variable 'active_layers' set but not used [-Werror,-Wunused-but-set-variable]
	        int active_layers = 0, pre_ber_layers = 0, post_ber_layers = 0;
	            ^
	1 error generated.

Link: https://lore.kernel.org/linux-media/20230628130339.206261-1-mchehab@kernel.org


Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>