ext2: Drop GFP_NOFS allocation from ext2_init_block_alloc_info()

The allocation happens under inode->i_rwsem and
EXT2_I(inode)->i_truncate_mutex. Neither of them is acquired during
direct fs reclaim so the allocation can be changed to GFP_KERNEL.

Signed-off-by: Jan Kara <jack@suse.cz>