trivial.  correct a misleading comment.

Reference: /n/sources/patch/applied/sysfilecmt
Date: Thu Jun  2 23:41:22 CES 2011
Signed-off-by: quanstro@quanstro.net

--- /sys/src/9/port/sysfile.c	Thu Jun  2 23:40:14 2011
+++ /sys/src/9/port/sysfile.c	Thu Jun  2 23:40:12 2011
@@ -31,7 +31,7 @@
 	if(fd >= f->nfd+DELTAFD)
 		return -1;	/* out of range */
 	/*
-	 * Unbounded allocation is unwise; besides, there are only 16 bits
+	 * Unbounded allocation is unwise; besides, there are only 32 bits
 	 * of fid in 9P
 	 */
 	if(f->nfd >= 5000){