pci: avoid memory leak

pci: avoid memory leak

strdup uses malloc to allocate memory for str.
If we cannot bind to the generic driver we should release
the memory.

The problem was indicated by clang scan-build.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>