fortran: Remove default initialization of local pointers's span

fortran: Remove default initialization of local pointers's span

A pointer has no default initialization; it is invalid to use it before
it is associated to a target.  We can just as well leave its span field
uninitialized, and wait for the first pointer association to define a
span value.  The value of zero was an invalid span value anyway.

gcc/fortran/ChangeLog:

	* trans-decl.cc (gfc_trans_deferred_vars): Don't default
	initialize the span of local pointer arrays.