doc: Build-win32: Improve incorrect navigation path to vlc

VLC is building inside the "Build" folder as per Build-win32

The hierarchy is as follows:

|-VLC
 |-bin
 |-build
 |-contribs
 |-others...

Build-win32 is using "../vlc/extras/package/win32/build.sh -a x86_64" to run build.sh and other scripts inside Build folder. It means we first navigate to parent directory (../) i.e VLC and then again moving to vlc directory that is inside parent vlc, which is not present and throwing error:

   cd: ../vlc: No such file or directory

By this commit the issue is resolved. Now we are directing towards the correct directory.

vlc(parent) -> build -> run scripts "../extras/package" -> vlc(parent) -> extras -> ...

Fixes: #28562 (closed)