MAINTAINERS: fix the cm-t35 board name

"cm-t35" in U-Boot source code is called "cm_t35".
Make the change "cm-t35" -> "cm_t35" for better greppability.

Signed-off-by: Igor Grinberg <grinberg@compulab.co.il>

MAINTAINERS

@@ -684,7 +684,7 @@ Simon Guinot <simon.guinot@sequanux.org>
 
 Igor Grinberg <grinberg@compulab.co.il>
 
-	cm-t35		ARM ARMV7 (OMAP3xx Soc)
+	cm_t35		ARM ARMV7 (OMAP3xx Soc)
 
 Stefan Herbrechtsmeier <stefan@code.herbrechtsmeier.net>