speed up jiffies conversion functions if HZ==USER_HZ

Avoid calling do_div(x, 1) in this case.

Cc: David Fries <david@fries.net>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

kernel/time.c

@@ -606,8 +606,10 @@ u64 jiffies_64_to_clock_t(u64 x)
 # if HZ < USER_HZ
 	x *= USER_HZ;
 	do_div(x, HZ);
-# else
+# elif HZ > USER_HZ
 	do_div(x, HZ / USER_HZ);
+# else
+	/* Nothing to do */
 # endif
 #else
 	/*