Inlining generates an unknown _lpy_arg

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import loopy as lp
import numpy as np
child_knl = lp.make_function(
        [],
        """
        g[0] = 2*e[0] + 3*f[0]
        g[1] = 2*e[1] + 3*f[1]
        """, name="linear_combo")
parent_knl = lp.make_kernel(
        ["{[j]:0<=j<n}", "{[i]:0<=i<n}"],
        """
        [i]: z[i, j] = linear_combo([i]: x[i, j], [i]: y[i,j])
        """,
        kernel_data=[
            lp.GlobalArg(
                name="x, y, z",
                dtype=np.float64,
                shape=("n", "n")),
            ...],
        assumptions="n>=1",
        )
knl = lp.merge([parent_knl, child_knl])
knl = lp.inline_callable_kernel(knl, "linear_combo")
print(lp.generate_code_v2(knl).device_code())

Above program fails with TypeInferenceFailure: name not known in type inference: _lpy_arg

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cc @kaushikcfd

[inducer]

#648 is possibly related.