[package/base-files] hot-fix nameclash in sysupgrade: rename pivot() to supivot(...

[package/base-files] hot-fix nameclash in sysupgrade: rename pivot() to supivot() in sysupgrade

Sysupgrade defines its very own pivot() function.
Prior merging boot.sh and functions.sh sysupgrade just included boot.sh,
now it includes functions.sh which defines pivot() as well, however
slightly different which causes sysupgrade to fail.

This is a hot-fix to unbreak sysupgrade, however those two pivot()
functions should actually get merged.

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@34815 3c298f89-4303-0410-b956-a3cf2f4a3e73