pipe-loader: Fix build

pipe_loader_drm.c: In function 'pipe_loader_drm_probe_fd':
pipe_loader_drm.c:120:4: error: implicit declaration of function 'loader_get_pci_id_for_fd' [-Werror=implicit-function-declaration]

Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>

src/gallium/auxiliary/pipe-loader/pipe_loader_drm.c

@@ -41,6 +41,7 @@
 
 #endif
 
+#include "loader.h"
 #include "state_tracker/drm_driver.h"
 #include "pipe_loader_priv.h"