contrib: x262: fix cp call
The cp call is broken: cp x262/vlc_build/x264.h x262/vlc_build/x262.h cp: cannot stat 'x262/vlc_build/x264.h': No such file or directory make: *** [../src/x262/rules.mak:37: .x262] Error 1 x264.h isn't generated inside the build directory (x262/vlc_build), but exists in the x262 source directory. The install rules also install it from the source directory. Therefore, copy it from and to the source dir, not the build dir. Regression from 697a2fcd.