Fix tc358743 identifier in the /boot/config.txt population (#1617)

This fixes a small bug in the tinypilot.postinst that was preventing it
from matching the right line in `/boot/config.txt` to add the
`dtoverlay=tc358743-audio` line.

## Peer testing

To test this bundle run:

```bash
curl \
  --silent \
  --show-error \
  --location \
  https://raw.githubusercontent.com/tiny-pilot/tinypilot/master/scripts/install-bundle | \
  sudo bash -s -- \
    https://output.circle-artifacts.com/output/job/0bcd7da3-9a88-4126-ada8-6a7804e02dfe/artifacts/0/bundler/dist/tinypilot-community-20230901T1500Z-1.9.0-75+03827f4.tgz && \
  sudo reboot
```

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debian-pkg/debian/tinypilot.postinst

@@ -98,7 +98,7 @@ if grep --silent '^dtoverlay=tc358743$' "${BOOT_CONFIG_PATH}" ; then
   # Enable TC358743-audio overlay in /boot/config.txt.
   # Note that the tc358743-audio overlay depends on the tc358743 overlay.
   sed --in-place --expression '/dtoverlay=tc358743-audio/d' "${BOOT_CONFIG_PATH}"
-  sed --in-place '/dtoverlay=tc35843/ a dtoverlay=tc358743-audio' "${BOOT_CONFIG_PATH}"
+  sed --in-place '/dtoverlay=tc358743/ a dtoverlay=tc358743-audio' "${BOOT_CONFIG_PATH}"
 
   # Set GPU memory to 256MB in /boot/config.txt
   if grep --silent '^gpu_mem=' "${BOOT_CONFIG_PATH}" ; then