Fixed invocation of dh_shlibdeps when cross-compiling with
do_linux_tools=true.
Without being told where to find the crossdev libs, dh_shlibdeps
will emit these warnings and fail the linux-tools package:

  Debug: binary-acm7xxx
  ...
  dh_shlibdeps -plinux-headers-4.4.0-15-generic
  arm-linux-gnueabihf-objdump: .../asn1_compiler: File format not recognized
  arm-linux-gnueabihf-objdump: .../extract-cert: File format not recognized
  ...

For example:

archtriple=arm-linux-gnueabihf
         flavour=generic
         dpkg-architecture -t $archtriple -c fakeroot \
                debian/rules \
                binary-$flavour binary-perarch \
                AUTOBUILD=true \
                abi_suffix= \
                do_linux_tools=true \
                do_tools=true \
                do_tools_usbip=false \
                do_tools_cpupower=false \
                do_tools_perf=true \
                do_tools_x86=false
Signed-off-by: David Leonard <david.leonard@opengear.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>