Do not flush the wrong fifo

[bugadani]

When disabling an OUT endpoint, the previous implementation flushed a TX FIFO, but TX FIFOs are assigned to IN endpoints.

I think this closes (maybe not, though?) #5521 as the PR fixes an identical-looking issue on the ESP32-S3, and the F405 uses a different version of the same IP.

[Copilot]

Pull request overview

This PR fixes a bug in embassy-usb-synopsys-otg where disabling an OUT endpoint incorrectly triggered a TX FIFO flush — a TX FIFO operation that only makes sense for IN endpoints. The fix moves the TX FIFO flush logic from the Direction::Out branch to the Direction::In branch of endpoint_set_enabled, where it belongs, since TX FIFOs are allocated per-IN-endpoint on this hardware. This resolves a likely root cause for USB CDC NCM connectivity issues on STM32F405 (and similar Synopsys OTG-based chips).

Changes:

• Removes the TX FIFO flush from the OUT endpoint disable path
• Adds the TX FIFO flush (with wait loop) to the IN endpoint disable/enable path
• Documents the fix in the CHANGELOG

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
embassy-usb-synopsys-otg/src/lib.rs	Moves TX FIFO flush from Direction::Out to Direction::In branch in endpoint_set_enabled
embassy-usb-synopsys-otg/CHANGELOG.md	Adds changelog entry for the bug fix under the Unreleased section

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[kaspar030]

I confirm this fixes our issue on Linux where the esp32-s3 usb ethernet would not properly come up. With this fix, it works like a charm.