tools lib bpf: Fix double file test in Makefile

tools lib bpf: Fix double file test in Makefile

The Makefile verifies the same file exists twice:
  test -f ../../../include/uapi/linux/bpf.h -a \
       -f ../../../include/uapi/linux/bpf.h

The purpose of the check is to ensure the diff (immediately after the
test) doesn't fail with these two files:

  tools/include/uapi/linux/bpf.h
  include/uapi/linux/bpf.h

Same recipe for bpf_common:
  test -f ../../../include/uapi/linux/bpf_common.h -a \
       -f ../../../include/uapi/linux/bpf_common.h

This corrects the location of the tests.

Signed-off-by: Daniel Díaz <daniel.diaz@linaro.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1502814810-960-1-git-send-email-daniel.diaz@linaro.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>