HACK to work around a TLB exception when booting

When building the kernel with dev branch clang I get the following when
booting:
```
Trap cause = 2 (TLB miss (load or instr. fetch) - kernel mode)
[ thread pid 2 tid 100015 ]
Stopped at      ata_zac_mgmt_in+0x29c4: lbu     at,1016(v1)
```

The actual location is `path->device->inq_flags |= SID_DMA` inside
probefunc in ata_xpt.c. The crash doesn't happen with the nosp branch
but the only difference I can see in the generated code is that the dev
branch hoists the load of path->device before the if statement.
What's even weirder is that when I single step with GDB it will fail
when loading exactly the address that is printed by the printf().

sys/cam/ata/ata_xpt.c

@@ -459,6 +459,13 @@ probestart(struct cam_periph *periph, union ccb *start_ccb)
 		/* If SIM disagree - renegotiate. */
 		if (mode != wantmode)
 			goto negotiate;
+
+		/* XXXAR: without the printf the following load of
+		 *  path->device_inq_flags causes a TLB miss when compiled
+		 *  with the latest clang. Possibly there is some strict
+		 * aliasing error? */
+		printf("ata_xpt crash workaround: path=%p, path->device=%p\n",
+		    path, path->device);
 		/* Remember what transport thinks about DMA. */
 		if (mode < ATA_DMA)
 			path->device->inq_flags &= ~SID_DMA;