sysutils/uefi-edk2-bhyve: fix build with modern compilers

Since GCC11/Clang13, build was failed with error:
argument 2 of type 'const uint8_t *' {aka 'const unsigned char *'} declared as a pointer [-Werror=vla-parameter]

Backport patch from brotli upstream

While here, fix string pointer overflows in USB handler code [1]

PR: 263545
Approved by: portmgr blanket (Tier 1 fix build)
Obtained from: Gentoo bug#801925 [1]