genesys: Fix a potential buffer overread spotted by Coverity
genesys: Fix a potential buffer overread spotted by Coverity

overrun-buffer-arg: Overrunning array buf of 64 bytes by passing it to
a function which accesses it at byte offset 65 using argument len + 3UL

fwupd/fwupd,fwupd/fwupd,fwupd/fwupd,fwupd/fwupd