MAINTAINERS: Add dwc3-st.c file to ARCH/STI architecture

This patch adds the new dwc3-st.c glue driver found on
STMicroelectronics stih407 consumer electronics SoC's into the STI
arch section of the maintainers file.
Signed-off-by: Peter Griffin <peter.griffin@linaro.org>
Acked-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Felipe Balbi <balbi@ti.com>

MAINTAINERS

@@ -1392,6 +1392,7 @@ F:	drivers/media/rc/st_rc.c
 F:	drivers/i2c/busses/i2c-st.c
 F:	drivers/tty/serial/st-asc.c
 F:	drivers/mmc/host/sdhci-st.c
+F:	drivers/usb/dwc3/dwc3-st.c
 
 ARM/TECHNOLOGIC SYSTEMS TS7250 MACHINE SUPPORT
 M:	Lennert Buytenhek <kernel@wantstofly.org>