ext2fs_set_gdt_csum(): Force the last block group to have a valid block bitmap

ext2fs_set_gdt_csum(): Force the last block group to have a valid block bitmap

Never set the UNINIT_BLOCKS flag for the last group since the kernel
doesn't handle the case graefully if there is a full set of blocks in
each blockgroup marked UNINIT_BLOCKS.  The kernel should be fixed up,
but in the meantime this avoids hitting the problem, and is more
consistent with lazy_bg not marking the last group UNINIT.

Signed-off-by: Andreas Dilger <adilger@dilger.ca>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>