mx28: Fix elftosb source link in README.mx28_common

The documented link to elftosb package tarball is not accessible,
change to another working link.

Signed-off-by: Anatolij Gustschin <agust@denx.de>
Cc: Otavio Salvador <otavio@ossystems.com.br>
Cc: Marek Vasut <marek.vasut@gmail.com>
Cc: Fabio Estevam <festevam@gmail.com>
Acked-by: Otavio Salvador <otavio@ossystems.com.br>
Acked-by: Detlev Zundel <dzu@denx.de>
Acked-by: Marek Vasut <marex@denx.de>

doc/README.mx28_common

@@ -30,14 +30,14 @@ is the "mxsboot" tool found in U-Boot source tree.
 
 Firstly, obtain the elftosb archive from the following location:
 
-	http://foss.doredevelopment.dk/mirrors/imx/elftosb-10.12.01.tar.gz
+	ftp://ftp.denx.de/pub/tools/elftosb-10.12.01.tar.gz
 
 We use a $VER variable here to denote the current version. At the time of
 writing of this document, that is "10.12.01". To obtain the file from command
 line, use:
 
 	$ VER="10.12.01"
-	$ wget http://foss.doredevelopment.dk/mirrors/imx/elftosb-${VER}.tar.gz
+	$ wget ftp://ftp.denx.de/pub/tools/elftosb-${VER}.tar.gz
 
 Extract the file: