specify MODULE to avoid module .pri filename clash

specify MODULE to avoid module .pri filename clash

Since 733ac1f6e6b3155a594376ef99288c6117124000 the default MODULE
is the base of the .pro file for the plugin (i.e., "windows"). Since
MODULE becomes the base of the module .pri, the names of the module
.pri files can clash. Now we explicitly specify MODULE for
printersupport plugins to avoid overwriting the module .pri files of
the platform plugins whose .pro files have the same names.

Follow-up to 81f8f0db5cb75e29b041a011ca4e7dbbf2d903c5 which renamed the
TARGET.

Change-Id: Ie83892dc419257e1df3b81bcf6ecec751ae345b0
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>