x86: make early_console static in early_printk.c

Not necessary to expose it, also fixes sparse warning.

arch/x86/kernel/early_printk.c:196:16: warning: symbol 'early_console' was not declared. Should it be static?

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>