winsys/drm: Correctly install EGL drivers.

Remove extraneous quotes that prevent some drivers to be installed when
there are more than one display in EGL_DISPLAYS.
diff --git a/src/gallium/winsys/drm/Makefile.egl b/src/gallium/winsys/drm/Makefile.egl
index d79ceee..b1f2038 100644
--- a/src/gallium/winsys/drm/Makefile.egl
+++ b/src/gallium/winsys/drm/Makefile.egl
@@ -55,7 +55,7 @@
 
 install: $(EGL_DISPLAY_LIBS)
 	$(INSTALL) -d $(DESTDIR)$(EGL_DRIVER_INSTALL_DIR)
-	for lib in "$(EGL_DISPLAY_LIBS)"; do \
+	for lib in $(EGL_DISPLAY_LIBS); do \
 		$(MINSTALL) -m 755 "$$lib" $(DESTDIR)$(EGL_DRIVER_INSTALL_DIR); \
 	done