fix:Report the full buffer length to the UAC stack by setting bytes_r… (IDFGH-16855)

[KinhoLeung]

Description
Set bytes_read to len in usb_uac_device_input_cb() after a successful esp_codec_dev_read().
This ensures the UAC stack receives the correct number of bytes and no longer interprets the callback as producing zero-length audio data.

Related
N/A (found while testing the USB UAC device input callback).
Testing
Built the USB UAC example.
Ran on an ESP32-S4 board and verified that audio input is correctly received by the host (no more zero-length data reported).

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Note

Set bytes_read = len in usb_uac_device_input_cb so the UAC stack receives full-length audio data instead of zero-length.

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[github-actions]

Warnings

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Some issues found for the commit messages in this PR: the commit message "fix:Report the full buffer length to the UAC stack by setting bytes_read in usb_uac_device_input_cb(), so the host correctly detects received audio data instead of seeing zero bytes.": summary should not end with a period (full stop) summary looks empty type/action looks empty Please fix these commit messages - here are some basic tips: follow Conventional Commits style correct format of commit message should be: <type/action>(<scope/component>): <summary>, for example fix(esp32): Fixed startup timeout issue allowed types are: change,ci,docs,feat,fix,refactor,remove,revert,test sufficiently descriptive message summary should be between 20 to 72 characters and start with upper case letter avoid Jira references in commit messages (unavailable/irrelevant for our customers) TIP: Install pre-commit hooks and run this check when committing (uses the Conventional Precommit Linter).

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[cursor]

Bug: bytes_read not set on error path

When esp_codec_dev_read fails, the function returns early without setting *bytes_read. This leaves the output parameter uninitialized or containing stale data, potentially causing the caller to misinterpret how many bytes were actually read. The error path needs to set *bytes_read = 0 before returning to indicate no data was successfully read.