use the logical sector size to avoid having to deal with mbr
booting issues.  ideally this would be an x86-only hack.

Reference: /n/atom/patch/applied/uselogss
Date: Sat Mar  1 14:41:28 CET 2014
Signed-off-by: quanstro@quanstro.net

--- /sys/src/libfis/fis.c	Sat Mar  1 14:40:42 2014
+++ /sys/src/libfis/fis.c	Sat Mar  1 14:40:43 2014
@@ -1,11 +1,15 @@
 /*
  * sata fises and sas frames
- * copyright © 2009-2010 erik quanstrom
+ * copyright © 2009-2014 erik quanstrom
  */
 #include <u.h>
 #include <libc.h>
 #include <fis.h>
 
+enum{
+	Usepsec	= 0,		/* use physical sector size.  */
+};
+
 static char *flagname[9] = {
 	"lba",
 	"llba",
@@ -225,8 +229,6 @@
 	Idmasp	= 1<<8,
 	Ilbasp	= 1<<9,
 	Illba	= 1<<10,
-
-	Usepsec	= 1,
 };
 
 vlong
@@ -469,6 +471,7 @@
 		*n >>= f->physshift;
 		lba >>= f->physshift;
 	}
+	USED(f);
 
 	return lba;
 }