fix automatic resource file inclusion

Commit c7334fbc

 broke the automatic resource file inclusion.
qmake's exists function checks at the location of the .pri file,
not the location of the .pro file.

Change-Id: I54f1bc664c06c5675ef26341619142bc58f0831e
Reviewed-by: Andras Becsi <andras.becsi@theqtcompany.com>