Fortran: Fixes for pointer function call as variable (PR96896)

gcc/fortran/ChangeLog:

	PR fortran/96896
	* resolve.c (get_temp_from_expr): Also reset proc_pointer +
	use_assoc attribute.
	(resolve_ptr_fcn_assign): Use information from the LHS.

gcc/testsuite/ChangeLog:

	PR fortran/96896
	* gfortran.dg/ptr_func_assign_4.f08: Update dg-error.
	* gfortran.dg/ptr-func-3.f90: New test.