Do not use std::mem in VSX tests

Author: gnzlbg

crates/core_arch/src/powerpc/vsx.rs

@@ -93,7 +93,7 @@ mod tests {
 
     use crate::core_arch::simd::*;
     use stdsimd_test::simd_test;
-    use std::mem;
+    use super::mem;
 
     macro_rules! test_vec_xxpermdi {
         {$name:ident, $shorttype:ident, $longtype:ident, [$($a:expr),+], [$($b:expr),+], [$($c:expr),+], [$($d:expr),+]} => {