timekeeping: Fold in timekeeping_delta_to_ns()

timekeeping_delta_to_ns() is now called only from
timekeeping_cycles_to_ns(), and it is not useful otherwise.

Simplify the code by folding it into timekeeping_cycles_to_ns().

No functional change.
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20240325064023.2997-16-adrian.hunter@intel.com

kernel/time/timekeeping.c

@@ -364,23 +364,12 @@ static void tk_setup_internals(struct timekeeper *tk, struct clocksource *clock)
 }
 
 /* Timekeeper helper functions. */
-
-static inline u64 timekeeping_delta_to_ns(const struct tk_read_base *tkr, u64 delta)
-{
-	u64 nsec;
-
-	nsec = delta * tkr->mult + tkr->xtime_nsec;
-	nsec >>= tkr->shift;
-
-	return nsec;
-}
-
 static inline u64 timekeeping_cycles_to_ns(const struct tk_read_base *tkr, u64 cycles)
 {
 	/* Calculate the delta since the last update_wall_time() */
 	u64 delta = clocksource_delta(cycles, tkr->cycle_last, tkr->mask);
 
-	return timekeeping_delta_to_ns(tkr, delta);
+	return ((delta * tkr->mult) + tkr->xtime_nsec) >> tkr->shift;
 }
 
 static __always_inline u64 __timekeeping_get_ns(const struct tk_read_base *tkr)