Bug 1493916 - Fix ppc64 inline assembler for clang r=jcj

Seems clang's inline assembler doesn't want registers to be prefixed with "r",
while gcc accepts both - r0 and 0 for GPR0.

tested with clang 6.0 and gcc 8.1

--HG--
extra : amend_source : 87e09bb59c78bdb25b9573b9f29511e10b9db6fa
extra : histedit_source : 9b3fad70ac2851bf7de14d42c34db4a5fba41710

lib/freebl/mpi/mpcpucache.c

@@ -727,7 +727,7 @@ static inline void
 dcbzl(char *array)
 {
     register char *a asm("r2") = array;
-    __asm__ __volatile__("dcbzl %0,r0"
+    __asm__ __volatile__("dcbzl %0,0"
                          : "=r"(a)
                          : "0"(a));
 }