wifi: iwlwifi: limit printed string from FW file

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

wifi: iwlwifi: limit printed string from FW file

There's no guarantee here that the file is always with a

NUL-termination, so reading the string may read beyond the

end of the TLV. If that's the last TLV in the file, it can

perhaps even read beyond the end of the file buffer.

Fix that by limiting the print format to the size of the

buffer we have.