tools: PCI: Fix installation when `make tools/pci_install`

The commit c9a70787

 ("tools pci: Do not delete pcitest.sh in 'make clean'")
fixed a `make tools clean` issue and simultaneously brought a regression
to the installation process:

  for script in .../tools/pci/pcitest.sh; do	\
	install $script .../usr/usr/bin;	\
  done
  install: cannot stat '.../tools/pci/pcitest.sh': No such file or directory

Update the install commands to fix the remaining issue.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Kishon Vijay Abraham I <kishon@ti.com>
Cc: Jean-Jacques Hiblot <jjhiblot@ti.com>
Cc: Kishon Vijay Abraham I <kishon@ti.com>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>