Fix dvb frontend debug variable to be static, to avoid linker
errors:

drivers/built-in.o:(.data+0xf4b0): multiple definition of `debug'
arch/x86/kernel/built-in.o:(.kprobes.text+0x90): first defined here
ld: Warning: size of symbol `debug' changed from 85 in arch/x86/kernel/built-in.o to 4 in drivers/built-in.o

It would also be Good if arch/x86/kernel/entry_32.S didn't have a
non-static 'debug' symbol.  OTOH, it helps catch things like this one.
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>