Fix linux debug build

[simonhong]

Need to consider development channel name in channels.gni just to avoid gn error because
we started to set it as a channel name in debug build from brave/brave-browser#653.
This change doesn't affect anything because we don't make debug build package.

Close brave/brave-browser#654

Submitter Checklist:

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
• Ran git rebase -i to squash commits (if needed).
• Tagged reviewers and labelled the pull request as needed.
• Request a security/privacy review as needed.

Test Plan:

Try debug build in linux

Reviewer Checklist:

• New files have MPL-2.0 license header.
• Request a security/privacy review as needed.
• Adequate test coverage exists to prevent regressions

[bridiver]

I think this one needs @mbacchi as well

[mbacchi]

looks good to me!

[simonhong]

Thanks for checking. Ready to approve this? :)