libavcodec/ppc/mpegvideoencdsp.c: fix stack smashing in pix_norm1_altivec() and pix_sum_altivec()

The vec_ste calls were mistakenly changed to vec_vsx_st in c5ca76ad, which
caused stack smashing.

Changing them back fixes crashes on ppc64el, when configured with
--toolchain=hardened.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/ppc/mpegvideoencdsp.c

@@ -55,7 +55,7 @@ static int pix_norm1_altivec(uint8_t *pix, int line_size)
     /* Sum up the four partial sums, and put the result into s. */
     sum = vec_sums((vector signed int) sv, (vector signed int) zero);
     sum = vec_splat(sum, 3);
-    vec_vsx_st(sum, 0, &s);
+    vec_ste(sum, 0, &s);
     return s;
 }
 #else
@@ -113,7 +113,7 @@ static int pix_sum_altivec(uint8_t *pix, int line_size)
     /* Sum up the four partial sums, and put the result into s. */
     sumdiffs = vec_sums((vector signed int) sad, (vector signed int) zero);
     sumdiffs = vec_splat(sumdiffs, 3);
-    vec_vsx_st(sumdiffs, 0, &s);
+    vec_ste(sumdiffs, 0, &s);
     return s;
 }
 #else