ext4: properly handle error of ext4_init_block_bitmap in ext4_read_block_bitmap_nowait

ext4: properly handle error of ext4_init_block_bitmap in ext4_read_block_bitmap_nowait

We mark buffer_head of bitmap successfully initialized even error occurs
in ext4_init_block_bitmap. Although we will return error, we will get a
invalid buffer_head of bitmap from next ext4_read_block_bitmap_nowait
which is marked buffer_verified but not successfully initialized actually
in previous ext4_read_block_bitmap_nowait.
Fix this by only marking buffer_head successfully initialized if
ext4_init_block_bitmap successes.

Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Link: https://lore.kernel.org/r/20230221115919.1918161-2-shikemeng@huaweicloud.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>