babl: babl-fish-reference remove superfluous set of dst_img->type[0]

As reported by Rafał Mikrut, fixing issue #57.
7 jobs for master in 3 minutes and 56 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #1177820
latest-lcms

00:01:31

failed #1177851
latest-nolcms

00:02:24

failed #1177785
latest-lcms

00:02:12

failed #1177786
latest-nolcms

00:02:20

passed #1177821
latest-nolcms

00:01:17

passed #1177823
latest-nolcms

00:03:36

passed #1177849
latest-nolcms

00:03:25

 
Name Stage Failure
failed
latest-nolcms Build
FATAL: kernel too old
Running after_script
FATAL: kernel too old
Uploading artifacts for failed job
Uploading artifacts...
WARNING: _build/meson-logs: no matching files
ERROR: No files to upload
Cleaning up file based variables
ERROR: Job failed: exit code 127