Update gyp file to use src/platform2/common-mk

We are moving the packages built by platform2's ebuild into src/platform2.
We need packages to use src/platform2/common-mk instead of
src/platform/common-mk.

BUG=chromium:378554
TEST=emerge-daisy platform2
TEST=trybot run on daisy, link, mario and duck

CQ-DEPEND=CL:201938

Change-Id: Ib61405a8c507ae3aa686d29653033f5e7f969386
Reviewed-on: https://chromium-review.googlesource.com/201980
Tested-by: Bertrand Simonnet <[email protected]>
Reviewed-by: Prathmesh Prabhu <[email protected]>
Commit-Queue: Bertrand Simonnet <[email protected]>
Reviewed-by: Simon Que <[email protected]>
1 file changed