MAINTAINERS: add pwm to PolarFire SoC entry

Add the newly introduced pwm driver to the existing PolarFire SoC entry.
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

MAINTAINERS

@@ -18138,6 +18138,7 @@ F:	drivers/clk/microchip/clk-mpfs*.c
 F:	drivers/i2c/busses/i2c-microchip-corei2c.c
 F:	drivers/mailbox/mailbox-mpfs.c
 F:	drivers/pci/controller/pcie-microchip-host.c
+F:	drivers/pwm/pwm-microchip-core.c
 F:	drivers/reset/reset-mpfs.c
 F:	drivers/rtc/rtc-mpfs.c
 F:	drivers/soc/microchip/mpfs-sys-controller.c