ext4: remove redundant code in ext4_fill_super()

The previous sb_min_blocksize() has already set the block size.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: Mingming Cao <cmm@us.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>