x11/wf-shell: unbreak build after 1b744b687e87

meson.build:16:17: ERROR: Dependency lookup for wayfire with method 'pkgconfig' failed: Could not generate cflags for wayfire:
Package wlroots was not found in the pkg-config search path.
Perhaps you should add the directory containing `wlroots.pc'
to the PKG_CONFIG_PATH environment variable
Package 'wlroots', required by 'wayfire', not found