video: fbdev: smscufx: Fix null-ptr-deref in ufx_usb_probe()

In the Linux kernel, the following vulnerability has been resolved:

video: fbdev: smscufx: Fix null-ptr-deref in ufx_usb_probe()

I got a null-ptr-deref report:

BUG: kernel NULL pointer dereference, address: 0000000000000000

...

RIP: 0010:fb_destroy_modelist+0x38/0x100

...

Call Trace:

ufx_usb_probe.cold+0x2b5/0xac1 [smscufx]

usb_probe_interface+0x1aa/0x3c0 [usbcore]

really_probe+0x167/0x460

...

ret_from_fork+0x1f/0x30

If fb_alloc_cmap() fails in ufx_usb_probe(), fb_destroy_modelist() will

be called to destroy modelist in the error handling path. But modelist

has not been initialized yet, so it will result in null-ptr-deref.

Initialize modelist before calling fb_alloc_cmap() to fix this bug.