ext4: clean up ext4_ext_insert_extent() call in ext4_ext_map_blocks()

ext4: clean up ext4_ext_insert_extent() call in ext4_ext_map_blocks()

Now that the eofblocks code has been removed, we don't need to assign
0 to err before calling ext4_ext_insert_extent() since it will assign
a return value to ret anyway.  The variable free_on_err can be
eliminated and replaced by a reference to allocated_clusters which
clearly conveys the idea that newly allocated blocks should be freed
when recovering from an extent insertion failure.  The error handling
code itself should be restructured so that it errors out immediately on
an insertion failure in the case where no new blocks have been allocated
(bigalloc) rather than proceeding further into the mapping code.  The
initializer for fb_flags can also be rearranged for improved
readability.  Finally, insert a missing space in nearby code.

No known bugs are addressed by this patch - it's simply a cleanup.

Reviewed-by: Ritesh Harjani <riteshh@linux.ibm.com>
Signed-off-by: Eric Whitney <enwlinux@gmail.com>
Link: https://lore.kernel.org/r/20200311205033.25013-1-enwlinux@gmail.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>