printk: avoid warning when CONFIG_PRINTK is disabled

kernel/printk.c:72: warning: `saved_console_loglevel' defined but not used

Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>