ext2: add missing brelse in ext2_new_blocks()

Fix missing brelse of bitmap_bh in the case of retry.

Link: https://lore.kernel.org/r/20191022091738.9160-1-cgxu519@mykernel.net


Signed-off-by: Chengguang Xu <cgxu519@mykernel.net>
Signed-off-by: Jan Kara <jack@suse.cz>