Correct U-Boot upstream repository

The U-Boot source moves to https://source.denx.de/u-boot/u-boot.git
effective 2021-02-28.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/board/st/common/MAINTAINERS b/board/st/common/MAINTAINERS
index c4e0c5f..0c6db54 100644
--- a/board/st/common/MAINTAINERS
+++ b/board/st/common/MAINTAINERS
@@ -1,6 +1,6 @@
 ST BOARDS
 M:	Patrick Delaunay <patrick.delaunay@foss.st.com>
 L:	uboot-stm32@st-md-mailman.stormreply.com (moderated for non-subscribers)
-T:	git https://gitlab.denx.de/u-boot/custodians/u-boot-stm.git
+T:	git https://source.denx.de/u-boot/custodians/u-boot-stm.git
 S:	Maintained
 F:	board/st/common/