correct the description string handling in i/f tables

	because the i/f structure can be a void segment (a dseg)
	it may not reference literals

	because a literal in a void segment causes masmx
	to generate nothing in the middle of a load string
	containing many literals, displacing the literals
	following the literal which is not there

	i/f physical address and i/f description are now
	in i_f structure