x86/io_delay: Break instead of fallthrough in switch statement

The current code is fine since 'case CONFIG_IO_DELAY_TYPE_NONE'
does nothing, but scripts/checkpatch.pl complains about this:

warning: Possible switch case/default not preceded by break or fallthrough comment

I like break statement better than a fallthrough comment here.
It avoids the warning and clarify the code.

No behavior change is intended.

Signed-off-by: Masahiro Yamada <[e-mail]>
Cc: Borislav Petkov <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Ingo Molnar <[e-mail]>

arch/x86/kernel/io_delay.c

···
 		 * are shorter until calibrated):
 		 */
 		udelay(2);
+		break;
 	case CONFIG_IO_DELAY_TYPE_NONE:
 		break;
 	}