net: usb: lan78xx: Fix double free issue with interrupt buffer allocation

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

net: usb: lan78xx: Fix double free issue with interrupt buffer allocation

In lan78xx_probe(), the buffer `buf` was being freed twice: once

implicitly through `usb_free_urb(dev->urb_intr)` with the

`URB_FREE_BUFFER` flag and again explicitly by `kfree(buf)`. This caused

a double free issue.

To resolve this, reordered `kmalloc()` and `usb_alloc_urb()` calls to

simplify the initialization sequence and removed the redundant

`kfree(buf)`. Now, `buf` is allocated after `usb_alloc_urb()`, ensuring

it is correctly managed by `usb_fill_int_urb()` and freed by

`usb_free_urb()` as intended.