NAND: fix some strict-aliasing compiler warnings

Signed-off-by: Wolfgang Denk <wd@denx.de>
diff --git a/include/nand.h b/include/nand.h
index 3c0752e..247d346 100644
--- a/include/nand.h
+++ b/include/nand.h
@@ -34,22 +34,22 @@
 extern nand_info_t nand_info[];
 extern void nand_init(void);
 
-static inline int nand_read(nand_info_t *info, ulong ofs, ulong *len, u_char *buf)
+static inline int nand_read(nand_info_t *info, off_t ofs, size_t *len, u_char *buf)
 {
 	return info->read(info, ofs, *len, (size_t *)len, buf);
 }
 
-static inline int nand_write(nand_info_t *info, ulong ofs, ulong *len, u_char *buf)
+static inline int nand_write(nand_info_t *info, off_t ofs, size_t *len, u_char *buf)
 {
 	return info->write(info, ofs, *len, (size_t *)len, buf);
 }
 
-static inline int nand_block_isbad(nand_info_t *info, ulong ofs)
+static inline int nand_block_isbad(nand_info_t *info, off_t ofs)
 {
 	return info->block_isbad(info, ofs);
 }
 
-static inline int nand_erase(nand_info_t *info, ulong off, ulong size)
+static inline int nand_erase(nand_info_t *info, off_t off, size_t size)
 {
 	struct erase_info instr;