serial: st-asc: remove include of pm_runtime.h

st-asc driver doesn't use helpers from pm_runtime.h thus remove its
include.
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Link: https://lore.kernel.org/r/20220616140024.2081238-5-claudiu.beznea@microchip.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/st-asc.c

@@ -17,7 +17,6 @@
 #include <linux/tty_flip.h>
 #include <linux/delay.h>
 #include <linux/spinlock.h>
-#include <linux/pm_runtime.h>
 #include <linux/of.h>
 #include <linux/of_platform.h>
 #include <linux/serial_core.h>