msm-4.19: Fix build error

Use python environment variable instead of system defined "python" version.

See https://android.googlesource.com/platform/build/+/master/


Changes.md#PATH_Tools for more information.

Change-Id: I5c89d2b955a918fa0cfe1a5358dbb9eb42ac5b3f
Signed-off-by: Roopesh Rajashekharaiah Nataraja <roopeshr@codeaurora.org>
Signed-off-by: Venkata Narendra Kumar Gutta <vnkgutta@codeaurora.org>