Change ASSERT(!"...") to cmn_err(CE_PANIC, ...)

There are a handful of ASSERT(!"...")'s throughout the code base for
cases which should be impossible.  This patch converts them to use
cmn_err(CE_PANIC, ...) to ensure they are always enabled and so that
additional debugging is logged if they were to occur.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #1445

module/zfs/arc.c

@@ -2944,7 +2944,7 @@ arc_access(arc_buf_hdr_t *buf, kmutex_t *hash_lock)
 		DTRACE_PROBE1(new_state__mfu, arc_buf_hdr_t *, buf);
 		arc_change_state(arc_mfu, buf, hash_lock);
 	} else {
-		ASSERT(!"invalid arc state");
+		cmn_err(CE_PANIC, "invalid arc state 0x%p", buf->b_state);
 	}
 }