mvebu: fix default partition name
The firmware partition name is specifc to ipTIME NAS1dual and should not be
set globally.
Fixes: #16148
Fixes: 6ff970bb51f5 ("mvebu: add support for ipTIME NAS1dual")
Signed-off-by: Boris Krasnovskiy <[email protected]>
Link: https://github.com/openwrt/openwrt/pull/16690
Signed-off-by: Robert Marko <[email protected]>