ltq-vdsl-fw: replace backticks by $(...)

This replaces deprecated backticks by more versatile $(...) syntax.

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>

package/kernel/lantiq/ltq-vdsl-fw/src/vdsl_fw_install.sh

@@ -25,7 +25,7 @@ MD5_DSL="655442e31deaa42c9c68944869361ec0"
 	[ $? -eq 0 -a -f "${FW}" ] || exit 1
 }
 
-F=`md5sum -b ${FW} | cut -d" " -f1`
+F=$(md5sum -b ${FW} | cut -d" " -f1)
 [ "$F" = "${MD5_FW}" ] || {
 	echo "Failed to verify Firmware MD5"
 	exit 1
@@ -37,8 +37,8 @@ echo "Unpack and decompress w921v Firmware"
 w921v_fw_cutter
 [ $? -eq 0 ] || exit 1
 
-T=`md5sum -b ${FW_TAPI} | cut -d" " -f1`
-D=`md5sum -b ${FW_DSL} | cut -d" " -f1`
+T=$(md5sum -b ${FW_TAPI} | cut -d" " -f1)
+D=$(md5sum -b ${FW_DSL} | cut -d" " -f1)
 
 [ "$T" = "${MD5_TAPI}" -a "$D" = "${MD5_DSL}" ] || {
 	echo "Failed to verify MD5"