tools: PCI: Fix compiler warning in pcitest

Fix the following compiler warning in pcitest:

pcitest.c: In function main:
pcitest.c:214:4: warning: too many arguments for
format [-Wformat-extra-args]
    "usage: %s [options]\n"

Fixes: fbca0b28 ("tools: PCI: Add 'h' in optstring of getopt()")
Signed-off-by: Alan Mikhak <alan.mikhak@sifive.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Paul Walmsley <paul.walmsley@sifive.com>