staging: erofs: fix undefined LZ4_decompress_safe_partial()

It needs an explicit LZ4 library dependency
if lz4 compression is enabled, found by kbuild randconfig.

Reported-by: kbuild test robot <lkp@intel.com>
Fixes: 05f9d4a0 ("staging: erofs: use the new LZ4_decompress_safe_partial()")
Signed-off-by: Gao Xiang <hsiangkao@aol.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>