This patch converts some usage of ext4_fsblk_t to s64.  This is needed
so that some of the sign conversion works as expected in if loops.
Signed-off-by: NAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: NMingming Cao <cmm@us.ibm.com>
Signed-off-by: N"Theodore Ts'o" <tytso@mit.edu>