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

@@ -15,8 +15,10 @@ setenv bootlogo "false"
 
 setenv vendor "allwinner"
 
-# Remember the default u-boot fdtfile
-setenv deffdt_file ${fdtfile}
+# Remember the default fdtfile provided by u-boot and delete the vendor name
+if setexpr subfdt sub ${vendor}/ "" ${fdtfile};then
+	setenv deffdt_file ${subfdt}
+fi
 
 # Remember the default u-boot fdtdir
 setenv deffdt_dir "${prefix}dtb"
@@ -34,6 +36,12 @@ if test -e ${devtype} ${devnum} ${prefix}armbianEnv.txt; then
 	env import -t ${load_addr} ${filesize}
 fi
 
+# Delete the vendor's name from the fdtfile variable and record the result
+# after the file with the environment variables has been read
+if setexpr subfdt sub ${vendor}/ "" ${fdtfile};then
+	setenv fdtfile ${subfdt}
+fi
+
 # In this shell, we can only check the existence of the file.
 # Make a check of reasonable ways to find the dtb file.
 # Set the true value of the paths.