e2fsck: fix incorrect bbitmap checksum failure caused by integer overflow

e2fsck: fix incorrect bbitmap checksum failure caused by integer overflow

On a filesystem with more than 2^32 blocks, the block group checksum test will
fail because "i" (the group number) is a 32-bit quantity that is used to
calculate the group's block bitmap block number.  Unfortunately, "i" is not
automatically promoted to 64-bit for this calculation and overflows.  When this
happens, e2fsck will incorrectly report bitmap checksum errors.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>