libmach: fix whitespace.

R=rsc, r
CC=golang-dev
https://golang.org/cl/2149046
diff --git a/src/libmach/linux.c b/src/libmach/linux.c
index e4e2fd5..30b4da2 100644
--- a/src/libmach/linux.c
+++ b/src/libmach/linux.c
@@ -199,7 +199,7 @@
 	t = malloc(sizeof *t);
 	if(t == nil)
 		return nil;
-        memset(t, 0, sizeof *t);
+	memset(t, 0, sizeof *t);
 
 	thr[nthr++] = t;
 	if(pid == 0 && nthr > 0)