DOC: correct typo in extending ndimage with C

[mikofski]

• closes DOC: BUG: typo in ndimage LowLevelCallable tutorial example #9167
• LowLevelCallable should call get_transform() from compiled Python extension example.c

Corrected output:

>>> callback = LowLevelCallable(get_transform(), ptr)
>>> im = np.arange(12).reshape(4, 3).astype(np.float64)
>>> print(ndimage.geometric_transform(im, callback))

[[0.     0.     0.    ]
 [0.     1.3625 2.7375]
 [0.     4.8125 6.1875]
 [0.     8.2625 9.6375]]

For traceback see related issue.

[mikofski]

The test failure is due to doctest output mismatch, so it is unrelated. See #9187

[rgommers]

Thanks for the fix @mikofski