btrfs: rename btrfs_csum_file_blocks() to btrfs_insert_data_csums()

btrfs: rename btrfs_csum_file_blocks() to btrfs_insert_data_csums()

The function btrfs_csum_file_blocks() is a little confusing, unlike
btrfs_csum_one_bio(), it is not calculating the checksum of some file
blocks.

Instead it's just inserting the already calculated checksums into a given
root (can be a csum root or a log tree).

So rename it to btrfs_insert_data_csums() to reflect its behavior better.

Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>