stv0991: record defconfig ownership in MAINTAINERS

This commit fixes warnings reported by tools/genboardscfg.py.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Vikas Manocha <vikas.manocha@st.com>
Acked-by: Vikas Manocha <vikas.manocha@st.com>
diff --git a/board/st/stv0991/MAINTAINERS b/board/st/stv0991/MAINTAINERS
index 87221e9..e7a2cca 100644
--- a/board/st/stv0991/MAINTAINERS
+++ b/board/st/stv0991/MAINTAINERS
@@ -3,3 +3,4 @@
 S:	Maintained
 F:	board/st/stv0991/
 F:	include/configs/stv0991.h
+F:	configs/stv0991_defconfig