warp7: MAINTAINERS: Add warp7_secure_defconfig entry

Add warp7_secure_defconfig entry to avoid the following warning:

WARNING: no maintainers for 'warp7_secure'

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
diff --git a/board/warp7/MAINTAINERS b/board/warp7/MAINTAINERS
index 1d3ee29..0fc9746 100644
--- a/board/warp7/MAINTAINERS
+++ b/board/warp7/MAINTAINERS
@@ -4,3 +4,4 @@
 F:	board/warp7/
 F:	include/configs/warp7.h
 F:	configs/warp7_defconfig
+F:	configs/warp7_secure_defconfig