CVE-2026-74679: usb: gadget: f_ncm: Use unsigned int for ndp_index

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

usb: gadget: fncm: Use unsigned int for ndpindex

The variable ndpindex is declared as a signed integer, but it stores the return value of getncm(), which is unsigned.

A malicious host can supply a large offset that overflows the signed ndpindex, making it negative. Because ndpindex is compared against unsigned bounds, this negative value bypasses sanity checks and leads to an out-of-bounds read when calculating the address of the NDP block (ntbptr + ndpindex).

Fix this by changing ndpindex to unsigned int to ensure consistent unsigned comparisons throughout the function.