name the executable '9fs64fs' not '9fs64fs64'.

Reference: /n/atom/patch/applied2013/fs64stutter
Date: Mon Aug 26 04:03:33 CES 2013
Signed-off-by: quanstro@quanstro.net

--- /sys/src/fs/fs64/mkfile	Mon Aug 26 04:03:11 2013
+++ /sys/src/fs/fs64/mkfile	Mon Aug 26 04:03:12 2013
@@ -5,7 +5,7 @@
 objtype=386
 </$objtype/mkfile
 
-TARG=$p$CONF'fs64'
+TARG=$p$CONF'fs'
 
 DEV=\
 	apc.$O\