ext2: remove ext2_new_block()

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I7TN3J



--------------------------------

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>