[PR113354][LRA]: Fixing LRA failure on building MIPS GCC

My recent patch for PR112918 triggered a hidden bug in LRA on MIPS.  A
pseudo is matched to a register constraint and assigned to a hard
registers at the first constraint sub-pass but later it is matched to
X constraint.  Keeping this pseudo in the register (MD0) prevents to
use the same register for another pseudo in the insn and this results
in LRA failure.  The patch fixes this by spilling the pseudo at the
constraint subpass when the chosen alternative constraint not require
hard register anymore.

gcc/ChangeLog:

	PR middle-end/113354
	* lra-constraints.cc (curr_insn_transform): Spill pseudo only used
	in the insn if the corresponding operand does not require hard
	register anymore.