mm/damon: fix sparse warning for zero initializer

sparse warns about zero initializing an array with {0,}, change it to
the equivalent {0}.

Fixes the sparse warning:
mm/damon/tests/vaddr-kunit.h:69:47: warning: missing braces around initializer

Link: https://lkml.kernel.org/r/xriwklcwjpwcz7eiavo6f7envdar4jychhsk6sfkj5klaznb6b@j6vrvr2sxjht


Fixes: 17ccae8b ("mm/damon: add kunit tests")
Signed-off-by: Leo Stone <leocstone@gmail.com>
Reviewed-by: SeongJae Park <sj@kernel.org>
Cc: Jinjie Ruan <ruanjinjie@huawei.com>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>