Calling `switch_to_ramfs()` will not copy the gzip executable
(/bin/gzip) to ramfs, but `/bin/zcat` will call `/bin/gzip` when
package gzip is installed, instead of the busybox-supplied zcat.
This will cause `zcat` to fail to find `gzip`, then cause the
sysupgrade to fail. Adding the `busybox` prefix here will solve
the problem.
Signed-off-by: Chuck Fan <fanck0605@qq.com>
d374e2cdb4