DEVELOPERS: add the stm32f469_disco_xip_defconfig entry

Commit a3e3d9c19829 ("configs/stm32f469_disco_xip_defconfig: alternative
defconfig for XIP configurations") forgot to add the corresponding entry
in the DEVELOPERS file.

Signed-off-by: Dario Binacchi <dariobin@libero.it>
Cc: Christophe Priouzeau <christophe.priouzeau@foss.st.com>
Cc: Yauheni Saldatsenka <eugentoo@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>

DEVELOPERS

@@ -531,6 +531,7 @@ F:	board/stmicroelectronics/stm32f429-disco/
 F:	board/stmicroelectronics/stm32f469-disco/
 F:	configs/stm32f429_disco_xip_defconfig
 F:	configs/stm32f469_disco_sd_defconfig
+F:	configs/stm32f469_disco_xip_defconfig
 
 N:	Christophe Vu-Brugier <cvubrugier@fastmail.fm>
 F:	package/drbd-utils/