dwarf2read: Make dwo_file::dbfd a gdb_bfd_ref_ptr

This removes the manual call to gdb_bfd_ref in favor of gdb_bfd_ref_ptr.

gdb/ChangeLog:

	* dwarf2read.c (struct dwo_file) <dbfd>: Change type to
	gdb_bfd_ref_ptr.
	<~dwo_file>: Remove call to gdb_bfd_unref.
	(open_and_init_dwo_file): Move gdb_bfd_ref_ptr into dbfd field. Call
	gdb_bfd_ref_ptr::get.
2 files changed