MAINTAINERS: Add stm32 mailbox IPPC driver

Signed-off-by: Fabien Dessenne <fabien.dessenne@st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@st.com>
diff --git a/MAINTAINERS b/MAINTAINERS
index e916841..bb0969c 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -301,6 +301,7 @@
 F:	arch/arm/mach-stm32mp/
 F:	drivers/clk/clk_stm32mp1.c
 F:	drivers/i2c/stm32f7_i2c.c
+F:	drivers/mailbox/stm32-ipcc.c
 F:	drivers/misc/stm32mp_fuse.c
 F:	drivers/mmc/stm32_sdmmc2.c
 F:	drivers/phy/phy-stm32-usbphyc.c