update mips cancellation-point syscall asm with 7-arg and r25 fixes

these fixes were already made to the normal syscall asm but not the
cancellation point version.

src/thread/mips/syscall_cp.s

@@ -7,17 +7,20 @@ __syscall_cp_asm:
 __cp_begin:
 	lw      $4, 0($4)
 	bne     $4, $0, 2f
-	move    $25, $5
+	move    $2, $5
 	move    $4, $6
 	move    $5, $7
 	lw      $6, 16($sp)
 	lw      $7, 20($sp)
 	lw      $8, 24($sp)
 	lw      $9, 28($sp)
+	lw      $10,32($sp)
 	subu    $sp, $sp, 32
 	sw      $8, 16($sp)
 	sw      $9, 20($sp)
-	move    $2, $25
+	sw      $10,24($sp)
+	sw      $2, 28($sp)
+	lw      $2, 28($sp)
 	syscall
 .global __cp_end
 __cp_end: