elm_atspi_bridge: Use narrower index types

elm_atspi_bridge: Use narrower index types

This patch changes `long` to `int` for indices. They either come from other
`int`-typed variables or from the literal value zero, and are further passed
to functions which expect an `int` parameter (possibly unsigned, but values
nearing 2^31 are purely theoretical, so it should never be a problem).

Change-Id: I5b110f308cd63b692b3f616f2d999e5e6b56cb09