powerpc/sstep: Avoid used uninitialized error

Older compilers think val may be used uninitialized:

  arch/powerpc/lib/sstep.c: In function 'emulate_loadstore':
  arch/powerpc/lib/sstep.c:2758:23: error: 'val' may be used uninitialized in this function

We know better, but initialise val to 0 to avoid breaking the build.
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/lib/sstep.c

@@ -2727,6 +2727,7 @@ int emulate_loadstore(struct pt_regs *regs, struct instruction_op *op)
 		if (!address_ok(regs, ea, size))
 			return -EFAULT;
 		err = 0;
+		val = 0;
 		switch (size) {
 #ifdef __powerpc64__
 		case 1: