ghostscript: set correct font path on target

ghostscript: set correct font path on target

GHOSTSCRIPT_FONTS_TARGET_DIR is set to $(TARGET_DIR)/usr/share/fonts/gs
in ghostscript-fonts.mk. If we pass this full path to ghostscript, it
will look for fonts in $(TARGET_DIR), which doesn't exist on the
target.

Instead of /usr/share/fonts/gs, use /usr/share/fonts so ghostscript can
also access other fonts than the ones installed by ghostscript-fonts.

Signed-off-by: Thomas Ehrhardt <tehrhardt@innovaphone.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>