Do not overwrite the buffer on writes.

Even Lords make brown paper bag mistakes. This is a left over code from my
initial testing, where the buffer where set with pre existing values to make
sure they were going through.  I forgot to remove them. As a result reads were
fine, but writes would just wipe the previous data from the buffer.
Incidentally, the "write-then-read-the-data-back" test I was doing would also
obviously pass, so I haven't noticed this so far.

Fix is to just leave the buffer alone.

bsd/porting/bus_dma.cc

@@ -109,9 +109,7 @@ bus_dmamap_load(bus_dma_tag_t dmat, bus_dmamap_t map, void *buf,
 		void *callback_arg, int flags)
 {
     unsigned int nsegs = 0;
-    for (unsigned int i = 0; i < buflen / sizeof(int); i++) {
-        ((unsigned int *)buf)[i] = i;
-    }
+
     while (buflen > 0) {
         auto segsize = std::min(buflen, dmat->maxsegsz);
         segsize = align_up(segsize, dmat->alignment);