[PATCH] __mod_timer: simplify ->base changing

Since base and new_base are of the same type now, we can save one 'if'
branch and simplify the code a bit.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>