MAINTAINERS: add missing STM32 entry

Signed-off-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: NThomas Huth <thuth@redhat.com>
Reviewed-by: NAlistair Francis <alistair@alistair23.me>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

MAINTAINERS

@@ -552,6 +552,7 @@ F: hw/char/stm32f2xx_usart.c
 F: hw/timer/stm32f2xx_timer.c
 F: hw/adc/*
 F: hw/ssi/stm32f2xx_spi.c
+F: include/hw/*/stm32*.h
 
 Netduino 2
 M: Alistair Francis <alistair@alistair23.me>