MIPS/BFD: Propagate the return status in attribute merging
    
    Fix the issue of any failure from `_bfd_elf_merge_object_attributes' not
    being propagated by `mips_elf_merge_obj_attributes'.
    
    	bfd/
    	* elfxx-mips.c (mips_elf_merge_obj_attributes): Propagate the
    	return status from `_bfd_elf_merge_object_attributes'.