Fix do_install issue for freetype-native

Fix do_install issue for freetype-native

The TOP_DIR is wrong in case native compile.
The value of PN=freetype-native. It causes do_install
error. This is error log of the issue

install: cannot stat
'...build/tmp/work/x86_64-linux/freetype-native/2.6-r0/ft2demos-2.6/bin/ftbench':
No such file or directory
(virtual:native: .../freetype_2.6.bb,do_install) failed with exit code '1'

This will change to use BPN instead of PN. BPN=freetype in both native
and cross compile.

Tested OK with bitbake freetype freetype-native.

Change-Id: I5a2b5bcc80755165ba026aedd177d03bc3f0e4a5
Signed-off-by: Phong Tran <tranmanphong@gmail.com>