iio: test : check null return of kunit_kmalloc in iio_rescale_test_scale

kunit_kmalloc may fail, return value might be NULL and will cause
NULL pointer dereference.Add KUNIT_ASSERT_NOT_ERR_OR_NULL fix it.

Signed-off-by: Pei Xiao <xiaopei01@kylinos.cn>
Fixes: 8e74a48 ("iio: test: add basic tests for the iio-rescale driver")
Link: https://patch.msgid.link/ecd56a85e54a96c2f0313c114075a21a76071ea2.1730259869.git.xiaopei01@kylinos.cn
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/test/iio-test-rescale.c

@@ -652,6 +652,8 @@ static void iio_rescale_test_scale(struct kunit *test)
 	int rel_ppm;
 	int ret;
 
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, buff);
+
 	rescale.numerator = t->numerator;
 	rescale.denominator = t->denominator;
 	rescale.offset = t->offset;
@@ -681,6 +683,8 @@ static void iio_rescale_test_offset(struct kunit *test)
 	int values[2];
 	int ret;
 
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, buff_off);
+
 	rescale.numerator = t->numerator;
 	rescale.denominator = t->denominator;
 	rescale.offset = t->offset;