kunit: fix kernel-doc warnings due to mismatched arg names

Commit 7122debb ("kunit: introduce
kunit_kmalloc_array/kunit_kcalloc() helpers") added new functions but
called last arg `flags`, unlike the existing code that used `gfp`.
This only is an issue in test.h, test.c still used `gfp`.

But the documentation was copy-pasted with the old names, leading to
kernel-doc warnings.

Do s/flags/gfp to make the names consistent and fix the warnings.

Fixes: 7122debb ("kunit: introduce kunit_kmalloc_array/kunit_kcalloc() helpers")
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Daniel Latypov <dlatypov@google.com>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Brendan Higgins <brendanhiggins@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>