mips gas: expression initialisation

mips gas: expression initialisation

There is a make_expr_symbol in append_insn, which gets called from
macro_build, which is all over the place.  Many of these set up an
expression without initialising all fields.  Now the uninitialised
fields should not be accessed in a properly functioning assembler,
but I'm inclined to think anything copied ought to be initialised.

	* config/tc-mips.c (fix_loongson2f_jump, load_register),
	(add_got_offset, add_got_offset_hilo, macro_build_branch_likely),
	(macro, mips16_macro, s_cpload, s_cpsetup, s_cprestore)
	(s_cpreturn): Use structure initialiser to ensure all fields of
	expression are initialised.
	(load_address): Copy entire structure for the same reason.