uvesafb ConnectorCallback Leak

Vulnerability analysis

The uvesafb framebuffer driver registers a connector callback for communication with a userspace daemon during module initialization, but if a subsequent platform driver registration step fails, the function returns without unregistering that callback. When the module is then unloaded by the kernel, the connector subsystem retains a pointer to the now-freed callback code. Any connector message arriving afterward causes the kernel to jump to unmapped memory, resulting in a panic. The fix adds the missing callback unregistration in the early error path, matching the cleanup already present in the later failure path. This issue is reachable only on systems where the uvesafb module is loaded, which requires root or boot-time configuration, and the dangling callback is triggered by a local connector message after a failed module initialization.