YAFFS2: fs/yaffs2/yaffs_nand.[hc] - fix build warnings

Fix these:
yaffs_guts.c: In function 'yaffs_Scan':
yaffs_guts.c:5436: warning: pointer targets in passing argument 4 of 'yaffs_QueryInitialBlockState' differ in signedness
yaffs_guts.c: In function 'yaffs_ScanBackwards':
yaffs_guts.c:6017: warning: pointer targets in passing argument 4 of 'yaffs_QueryInitialBlockState' differ in signedness
yaffs_nand.c: In function 'yaffs_QueryInitialBlockState':
yaffs_nand.c:109: warning: pointer targets in passing argument 4 of 'dev->queryNANDBlock' differ in signedness
yaffs_nand.c:113: warning: pointer targets in passing argument 4 of 'yaffs_TagsCompatabilityQueryNANDBlock' differ in signedness

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