[MIPS] RFA: Use new rtl iterators in r10k_needs_protection_p_1

[Matthew Fortune]

> gcc/
> 	* config/mips/mips.c (r10k_needs_protection_p_1): Take an rtx
> 	rather than an rtx pointer.  Change type of insn from "void *"
> 	to its real type.  Return bool rather than int.  Iterate over
> 	all subrtxes here.
> 	(r10k_needs_protection_p_store): Update accordingly.
> 	(r10k_needs_protection_p): Likewise.

OK