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.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>