fix busy() for Teensy4

[profezzorn]

Looks like there is a missing return statement.
This PR fixes that.

[Satak]

May I ask @PaulStoffregen why this PR was never merged? I asked copilot about this function and it gave similar suggestion.

The function int OctoWS2811::busy(void) has a potential bug due to an empty statement after the first if condition. Here is the problematic code:

if (!dma3.complete()) ; // DMA still running
if (micros() - update_begin_micros < numbytes * 10 + 300) return 1; // WS2812 reset
The first if condition checks if dma3 is complete but does nothing because of the semicolon (;). This means the function does not properly check if DMA is still running. Removing the semicolon should fix the issue:

if (!dma3.complete()) return 1; // DMA still running
if (micros() - update_begin_micros < numbytes * 10 + 300) return 1; // WS2812 reset
Now, the function will return 1 if DMA is still running or if the WS2812 reset time has not elapsed.