clocksource: vf_pit_timer: Use linux/sched_clock.h

Commit 38ff87f7 (sched_clock: Make ARM's sched_clock generic for all
architectures) changed the header to <linux/sched_clock.h>, so adapt
it in order to fix the following build error:

drivers/clocksource/vf_pit_timer.c:15:29: fatal error: asm/sched_clock.h: No such file or directory

Signed-off-by: Fabio Estevam <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Thomas Gleixner <[e-mail]>

drivers/clocksource/vf_pit_timer.c

···
 #include <linux/clk.h>
 #include <linux/of_address.h>
 #include <linux/of_irq.h>
-#include <asm/sched_clock.h>
+#include <linux/sched_clock.h>
 
 /*
  * Each pit takes 0x10 Bytes register space