ramips: mt7621: fix broken hexdump expression in iodata.sh

ramips: mt7621: fix broken hexdump expression in iodata.sh

Use the "1/1" as a iteration count of hexdump expression instead of the
broken "1", to fix the issue that the invalid bootnum will be obtained.

Currently, the hexdump command always outputs "0" when the decimal format
and the iteration count "1" are specified[0]. This is unexpected
behaviour, but the cause is unknown and use this fix as a workaround.

[0]: https://github.com/openwrt/openwrt/issues/18808

Signed-off-by: INAGAKI Hiroshi <musashino.open@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/18827
Signed-off-by: Robert Marko <robimarko@gmail.com>