ext2: remove ext2_new_block()

Now, only xattr allocate block use ext2_new_block(), so just opencode it in
the xattr code.

Signed-off-by: Ye Bin <yebin10@huawei.com>
Message-Id: <20230815112612.221145-2-yebin10@huawei.com>
Signed-off-by: Jan Kara <jack@suse.cz>