x86/tsc: Get rid of custom DIV_ROUND() macro

When invoced for positive values, DIV_ROUND macro defined in
arch/x86/kernel/tsc.c behaves exactly like DIV_ROUND_CLOSEST from
include/linux/kernel.h file, so remove the custom macro in favour
of the shared one.

[ hpa: changed line breaks ]

Signed-off-by: Michal Nazarewicz <mina86@mina86.com>
Link: http://lkml.kernel.org/r/1403143116-21755-1-git-send-email-mina86@mina86.com
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>