ramips: mt76x8: fix bootcount init script file permissions

The bootcount init script is missing the executable bit (644 instead of 755),
causing the script to not be executable:

  /etc/preinit: line 44: /etc/init.d/bootcount: Permission denied

Fixes: c3b8108 ("ramips: Add support for Xiaomi MiWiFi 3A")
Signed-off-by: Oliver Sedlbauer <os@dev.tdt.de>
Link: openwrt/openwrt#22446
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
(cherry picked from commit a15b224)

Author: osedlbauer