sparc: vDSO: Silence an uninitialized variable warning

Smatch complains that "val" would be uninitialized if kstrtoul() fails.

Fixes: 9a08862a

 ("vDSO for sparc")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>