Drop local lable from ppc asm timer.

The aix assembler does not support local lables.

libavutil/ppc/timer.h

@@ -31,12 +31,11 @@ static inline uint64_t read_time(void)
 
      /* from section 2.2.1 of the 32-bit PowerPC PEM */
      __asm__ volatile(
-         "1:\n"
          "mftbu  %2\n"
          "mftb   %0\n"
          "mftbu  %1\n"
          "cmpw   %2,%1\n"
-         "bne    1b\n"
+         "bne    $-0x10\n"
      : "=r"(tbl), "=r"(tbu), "=r"(temp)
      :
      : "cc");