e2fsck: optimize CPU usage in check_{block,inode}_bitmaps()

e2fsck: optimize CPU usage in check_{block,inode}_bitmaps()

The boolean expression (!skip_group || csum_flag) is always true,
since if csum_flag is FALSE, skip_group must also be FALSE.  Hence, we
can just remove the expression from the conditional altogether, thus
simplifying the code and making it easier to read/understand.

Also, in the case where the bit is set in the bitmap, there's no point
repeatedly setting first_free to be ext2fs_block_count(fs->super).

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>