s390x: replace nop with "nop 0" in inline assembly

... as a bandaid for building with clang until LLVM's internal assembler
supports nops without operand.

Signed-off-by: Marius Hillenbrand <mhillen@linux.ibm.com>

kernel/zarch/dgemv_t_4.c

@@ -438,7 +438,7 @@ static void add_y_kernel_4(BLASLONG n, FLOAT da, FLOAT *src, FLOAT *dest) {
     "agfi   %%r1,32\n\t"
     "brctg  %%r0,2b\n\t"
     "3:\n\t"
-    "nop"
+    "nop 0"
     : "+m"(*(struct { FLOAT x[n]; } *) dest)
     : [dest] "a"(dest),[da] "Q"(da), "m"(*(const struct { FLOAT x[n]; } *) src),
        [src] "a"(src),[n] "r"(n)