YAFFS2: fs/yaffs2/yaffs_guts.c - fix build warnings

Fix these:
yaffs_guts.c: In function 'yaffs_ReadDataFromFile':
yaffs_guts.c:4622: warning: pointer targets in passing argument 3 of 'yaffs_AddrToChunk' differ in signedness
yaffs_guts.c:4622: warning: pointer targets in passing argument 4 of 'yaffs_AddrToChunk' differ in signedness
yaffs_guts.c: In function 'yaffs_WriteDataToFile':
yaffs_guts.c:4745: warning: pointer targets in passing argument 3 of 'yaffs_AddrToChunk' differ in signedness
yaffs_guts.c:4745: warning: pointer targets in passing argument 4 of 'yaffs_AddrToChunk' differ in signedness
yaffs_guts.c: In function 'yaffs_ResizeFile':
yaffs_guts.c:4968: warning: pointer targets in passing argument 3 of 'yaffs_AddrToChunk' differ in signedness
yaffs_guts.c:4968: warning: pointer targets in passing argument 4 of 'yaffs_AddrToChunk' differ in signedness
yaffs_guts.c: In function 'yaffs_GutsInitialise':
yaffs_guts.c:7235: warning: assignment from incompatible pointer type
yaffs_guts.c: In function 'yaffs_CreateNewObject':
yaffs_guts.c:2143: warning: 'tn' may be used uninitialized in this function
yaffs_guts.c: In function 'yaffs_MknodObject':
yaffs_guts.c:2258: warning: 'str' may be used uninitialized in this function

Signed-off-by: Wolfgang Denk <wd@denx.de>