ppc: idctdsp: Immediately return if no AltiVec is available

This is how all the other init functions operate.

libavcodec/ppc/idctdsp.c

@@ -231,7 +231,9 @@ av_cold void ff_idctdsp_init_ppc(IDCTDSPContext *c, AVCodecContext *avctx,
                                  unsigned high_bit_depth)
 {
 #if HAVE_ALTIVEC
-    if (PPC_ALTIVEC(av_get_cpu_flags())) {
+    if (!PPC_ALTIVEC(av_get_cpu_flags()))
+        return;
+
     if (!high_bit_depth) {
         if ((avctx->idct_algo == FF_IDCT_AUTO) ||
             (avctx->idct_algo == FF_IDCT_ALTIVEC)) {
@@ -240,6 +242,5 @@ av_cold void ff_idctdsp_init_ppc(IDCTDSPContext *c, AVCodecContext *avctx,
             c->perm_type = FF_IDCT_PERM_TRANSPOSE;
         }
     }
-    }
 #endif /* HAVE_ALTIVEC */
 }