bootscript: Remove vendor name and slash from DTB file name

After that, the script successfully loads the DTB file from
two possible paths and overlays. If the file does not exist,
then the default file will be uploaded.

config/bootscripts/boot-sun50i-next.cmd

@@ -16,7 +16,11 @@ setenv bootlogo "false"
 setenv vendor "allwinner"
 
 # Remember the default u-boot fdtfile
-setenv deffdt_file ${fdtfile}
+if setexpr subfdt sub ${vendor}/ "" ${fdtfile};then
+	setenv deffdt_file ${subfdt}
+else
+	setenv deffdt_file ${fdtfile}
+fi
 
 # Remember the default u-boot fdtdir
 setenv deffdt_dir "${prefix}dtb"