Fix error introduced in 940dd94

We re-applied an earlier backport on code that had been modified since and properly fixed (ffmpeg commit 6e4a35c)

mythtv/external/FFmpeg/libavcodec/ppc/asm.S

@@ -70,11 +70,7 @@ X(\name):
 
 .macro movrel rd, sym, gp
 #if CONFIG_PIC
-    bcl             20, 31, lab_pic_\@
-lab_pic_\@:
-    mflr    \rd
-    addis   \rd, \rd, (\sym - lab_pic_\@)@ha
-    addi    \rd, \rd, (\sym - lab_pic_\@)@l
+    lwz     \rd, \sym@got(\gp)
 #else
     lis     \rd, \sym@ha
     la      \rd, \sym@l(\rd)