uvm_swap: a simple LIST_FOREACH conversion

[Theo Buehler]

I'd like to commit a few easy diffs to reduce differences to NetBSD in
UVM. This makes code comparison easier and also reduces the amount of
noise in WIP diffs I have for ongoing work on locking in UVM.

Here's a first one that converts a for loop to LIST_FOREACH:

Index: uvm/uvm_swap.c
===================================================================
RCS file: /cvs/src/sys/uvm/uvm_swap.c,v
retrieving revision 1.150
diff -u -p -r1.150 uvm_swap.c
--- uvm/uvm_swap.c      26 Mar 2021 13:40:05 -0000      1.150
+++ uvm/uvm_swap.c      10 Nov 2021 04:51:38 -0000
@@ -455,8 +455,8 @@ swaplist_insert(struct swapdev *sdp, str
        /*
         * find entry at or after which to insert the new device.
         */
-       for (pspp = NULL, spp = LIST_FIRST(&swap_priority); spp != NULL;
-            spp = LIST_NEXT(spp, spi_swappri)) {
+       pspp = NULL;
+       LIST_FOREACH(spp, &swap_priority, spi_swappri) {
                if (priority <= spp->spi_priority)
                        break;
                pspp = spp;