ch32f1: Fixed hanging gdb load command for CH32F103C8T6 MCU's

[lasutek]

Detailed description

It looks like a bug did slip into the code during refactoring of file src/target/ch32f1.c (commit 85cade5).

Fix: Added missing logical not operator (!) to function ch32f1_flash_eop_wait().

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• I've read the Code of Conduct
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• It builds for hardware native (see Building the firmware)
• It builds as BMDA (see Building the BMDA)
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Closing issues

[dragonmux]

LGTM, merging. Thank you for the contribution! You are indeed correct that check was supposed to loop while EOP is not set.