btrfs: scrub: also report errors hit during the initial read

[BUG]
After the recent scrub rework introduced in commit e02ee89b ("btrfs:
scrub: switch scrub_simple_mirror() to scrub_stripe infrastructure"),
btrfs scrub no longer reports repaired errors any more:

  # mkfs.btrfs -f $dev -d DUP
  # mount $dev $mnt
  # xfs_io -f -d -c "pwrite -b 64K -S 0xaa 0 64" $mnt/file
  # umount $dev
  # xfs_io -f -c "pwrite -S 0xff $phy1 64K" $dev # Corrupt the first mirror
  # mount $dev $mnt
  # btrfs scrub start -BR $mnt
  scrub done for 725e7cb7-8a4a-4c77-9f2a-86943619e218
  Scrub started:    Tue Jun  6 14:56:50 2023
  Status:           finished
  Duration:         0:00:00
  	data_extents_scrubbed: 2
  	tree_extents_scrubbed: 18
  	data_bytes_scrubbed: 131072
  	tree_bytes_scrubbed: 294912
  	read_errors: 0
  	csum_errors: 0 <<< No errors here
  	verify_errors: 0
         [...]
  	uncorrectable_errors: 0
  	unverified_errors: 0
  	corrected_errors: 16		<<< Only corrected errors
  	last_physical: 2723151872

This can confuse btrfs-progs, as it relies on the csum_errors to
determine if there is anything wrong.

While on v6.3.x kernels, the report is different:

 	csum_errors: 16			<<<
 	verify_errors: 0
	[...]
 	uncorrectable_errors: 0
 	unverified_errors: 0
 	corrected_errors: 16 <<<

[CAUSE]
In the reworked scrub, we update the scrub progress inside
scrub_stripe_report_errors(), using various bitmaps to update the
result.

For example for csum_errors, we use bitmap_weight() of
stripe->csum_error_bitmap.

Unfortunately at that stage, all error bitmaps (except
init_error_bitmap) are the result of the latest repair attempt, thus if
the stripe is fully repaired, those error bitmaps will all be empty,
resulting the above output mismatch.

To fix this, record the number of errors into stripe->init_nr_*_errors.
Since we don't really care about where those errors are, we only need to
record the number of errors.

Then in scrub_stripe_report_errors(), use those initial numbers to
update the progress other than using the latest error bitmaps.

Fixes: e02ee89b

 ("btrfs: scrub: switch scrub_simple_mirror() to scrub_stripe infrastructure")
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>