disk/mkfs,disk/mkext: fix mkdir conflict

R=rsc
http://codereview.appspot.com/6445076

src/cmd/disk/mkext.c

@@ -2,6 +2,8 @@
 #include <libc.h>
 #include <bio.h>
 
+#define mkdir plan9mkdir
+
 enum{
 	LEN	= 8*1024,
 	NFLDS	= 6,		/* filename, modes, uid, gid, mtime, bytes */

src/cmd/disk/mkfs.c

@@ -3,6 +3,7 @@
 #include <auth.h>
 #include <bio.h>
 
+#define mkdir plan9mkdir
 #define getmode plan9_getmode
 #define setuid plan9_setuid