powerpc/ftrace: Fix typo in mask of opcode

In commit 24a1bdc35, "Fix ABIv2 issues with __ftrace_make_call", Anton
changed the logic that checks for the expected code sequence when
patching a module.

We missed the typo in the mask, 0xffff00000 should be 0xffff0000, which
has the effect of making the test always true.

That makes it impossible to ftrace against modules, eg:

  Unexpected call sequence: 48000008 e8410018
  WARNING: at ../kernel/trace/ftrace.c:1638
  ftrace failed to modify [<d000000007cf001c>] rng_dev_open+0x1c/0x70 [rng_core]

Reported-by: David Binderman <dcb314@hotmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/kernel/ftrace.c

@@ -307,7 +307,7 @@ __ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 	 * The load offset is different depending on the ABI. For simplicity
 	 * just mask it out when doing the compare.
 	 */
-	if ((op[0] != 0x48000008) || ((op[1] & 0xffff00000) != 0xe8410000)) {
+	if ((op[0] != 0x48000008) || ((op[1] & 0xffff0000) != 0xe8410000)) {
 		printk(KERN_ERR "Unexpected call sequence: %x %x\n",
 			op[0], op[1]);
 		return -EINVAL;