Fix min / max value for 16 bit signed type

[preciz]

Fixes min / max value for 16 bit signed type, plus a small typo fix.

nx/exla/test/exla/defn/expr_test.exs

Lines 1108 to 1110 in 2f44f4a

	assert_equal(
	generic_as_type(non_finite, Nx.template({}, {:s, 16})),
	Nx.tensor([32767, 0, -32768], type: {:s, 16})

Thank you for reviewing.

[josevalim]

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