Fix stm32f3 application jump

[zvecr]

Checklist

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Description of Change

Was required for running qmk_firmware on top of the bootloader. Without this change it just produced:

[142696.720934] usb usb3-port2: attempt power cycle
[142697.190853] usb 3-2: new full-speed USB device number 117 using xhci_hcd
[142697.191129] usb 3-2: Device not responding to setup address.
[142697.397654] usb 3-2: Device not responding to setup address.
[142697.604181] usb 3-2: device not accepting address 117, error -71
[142697.727445] usb 3-2: new full-speed USB device number 118 using xhci_hcd
[142697.727746] usb 3-2: Device not responding to setup address.
[142697.934453] usb 3-2: Device not responding to setup address.
[142698.140727] usb 3-2: device not accepting address 118, error -71
[142698.140962] usb usb3-port2: unable to enumerate USB device
[142698.450804] usb 3-2: new full-speed USB device number 119 using xhci_hcd
[142698.640845] usb 3-2: device descriptor read/64, error -71
[142698.937660] usb 3-2: device descriptor read/64, error -71
[142699.234117] usb 3-2: new full-speed USB device number 120 using xhci_hcd
[142699.424292] usb 3-2: device descriptor read/64, error -71
[142699.657638] usb 3-2: device descriptor read/64, error -71
[142699.764223] usb usb3-port2: attempt power cycle

Code was borrowed from the f4 port.