board: MCR3000: Use lowercase filenames

Rename MCR3000.* to mcr3000.* to be more in line with
other boards.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
diff --git a/board/cssi/MAINTAINERS b/board/cssi/MAINTAINERS
index 7d237b0..e1c0baa 100644
--- a/board/cssi/MAINTAINERS
+++ b/board/cssi/MAINTAINERS
@@ -2,5 +2,5 @@
 M:	Christophe Leroy <christophe.leroy@csgroup.eu>
 S:	Maintained
 F:	board/cssi/
-F:	include/configs/MCR3000.h
+F:	include/configs/mcr3000.h
 F:	configs/MCR3000_defconfig