fortran: Remove premature initialization of a function result's span

fortran: Remove premature initialization of a function result's span

Setting just the span in an otherwise uninitialized array descriptor to
pass to a function that will use the descriptor for its result (thus do
the initialization) doesn't seem to be useful.

gcc/fortran/ChangeLog:

	* trans-array.cc (gfc_conv_expr_descriptor): Remove
	isolated initialization of the span field before passing to
	the function that will do the initialization.