mtd/sm_ftl.c: fix wrong do_div() usage

do_div() is meant to be used with an unsigned dividend.
Signed-off-by: Nicolas Pitre <nico@linaro.org>

drivers/mtd/sm_ftl.c

@@ -206,9 +206,10 @@ static loff_t sm_mkoffset(struct sm_ftl *ftl, int zone, int block, int boffset)
 }
 
 /* Breaks offset into parts */
-static void sm_break_offset(struct sm_ftl *ftl, loff_t offset,
+static void sm_break_offset(struct sm_ftl *ftl, loff_t loffset,
 			    int *zone, int *block, int *boffset)
 {
+	u64 offset = loffset;
 	*boffset = do_div(offset, ftl->block_size);
 	*block = do_div(offset, ftl->max_lba);
 	*zone = offset >= ftl->zone_count ? -1 : offset;