Fix warnings in yaffs

Fix warnings in yaffs

Sorry if this is already fixed somewhere - I could not find it.

This fixes the warnings show below.

yaffs_tagscompat.c: In function 'yaffs_TagsCompatabilityReadChunkWithTagsFromNAND':
yaffs_tagscompat.c:151: warning: dereferencing pointer 'tu' does break strict-aliasing rules
yaffs_tagscompat.c:150: warning: dereferencing pointer 'tu' does break strict-aliasing rules
yaffs_tagscompat.c:149: warning: dereferencing pointer 'tu' does break strict-aliasing rules
yaffs_tagscompat.c:148: warning: dereferencing pointer 'tu' does break strict-aliasing rules
yaffs_tagscompat.c:147: warning: dereferencing pointer 'tu' does break strict-aliasing rules
yaffs_tagscompat.c:146: warning: dereferencing pointer 'tu' does break strict-aliasing rules
yaffs_tagscompat.c:145: warning: dereferencing pointer 'tu' does break strict-aliasing rules
yaffs_tagscompat.c:144: warning: dereferencing pointer 'tu' does break strict-aliasing rules
yaffs_tagscompat.c:141: note: initialized from here

Signed-off-by: Simon Glass <sjg@chromium.org>