[BUG] broadcast of scalar array in last dimension fails after #1035

[davidkoski]

Describe the bug
broadcast of scalar array in last dimension fails after #1035

To Reproduce

Include code snippet

>>> import mlx.core as mx
>>> a = mx.zeros([2, 3, 4, 5, 3])
>>> a[..., 0] = 1
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: [expand_dims] Invalid axes 4 for output array with 1 dimensions.

Expected behavior

This should be able to broadcast the scalar array into the last dimension.

Desktop (please complete the following information):

• Version: commit hash 490c0c4