drm/tests: Fix incorrect argument in drm_test_mm_insert_range

While drm_mm test was converted form igt selftest to kunit, unexpected
value of "end" argument equal "start" was introduced to one of calls to a
function that executes the drm_test_mm_insert_range for specific start/end
pair of arguments.  As a consequence, DRM_MM_BUG_ON(end <= start) is
triggered.  Fix it by restoring the original value.

Fixes: fc8d29e2

 ("drm: selftest: convert drm_mm selftest to KUnit")
Signed-off-by: Janusz Krzysztofik <janusz.krzysztofik@linux.intel.com>
Cc: "Maíra Canal" <mairacanal@riseup.net>
Cc: Arthur Grillo <arthurgrillo@riseup.net>
Cc: Javier Martinez Canillas <javierm@redhat.com>
Cc: Daniel Latypov <dlatypov@google.com>
Cc: stable@vger.kernel.org # v6.1+
Reviewed-by: Maíra Canal <mairacanal@riseup.net>
Signed-off-by: Maíra Canal <mairacanal@riseup.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20230911130323.7037-2-janusz.krzysztofik@linux.intel.com