ar71xx: Speed up mtd extraction in ar71xx.sh

Although the amount of data read here is smaller than for the
caldata, there still might be some speed gain compared to reading
bytewise. And there is no harm ...

Signed-off-by: Adrian Schmutzler <[email protected]>

target/linux/ar71xx/base-files/lib/ar71xx.sh

@@ -16,7 +16,7 @@ ar71xx_get_mtd_offset_size_format() {
 	dev=$(find_mtd_part $mtd)
 	[ -z "$dev" ] && return
 
-	dd if=$dev bs=1 skip=$offset count=$size 2>/dev/null | hexdump -v -e "1/1 \"$format\""
+	dd if=$dev iflag=skip_bytes bs=$size skip=$offset count=1 2>/dev/null | hexdump -v -e "1/1 \"$format\""
 }
 
 ar71xx_get_mtd_part_magic() {
@@ -390,7 +390,7 @@ tplink_pharos_v2_get_model_string() {
 	part=$(find_mtd_part 'product-info')
 	[ -z "$part" ] && return 1
 
-	dd if=$part bs=1 skip=4360 count=64 2>/dev/null | tr -d '\r\0' | head -n 1
+	dd if=$part iflag=skip_bytes bs=64 skip=4360 count=1 2>/dev/null | tr -d '\r\0' | head -n 1
 }
 
 ar71xx_board_detect() {