of: of_pci.c needs export.h since it uses EXPORT_SYMBOLS

It was getting it implicitly before, since module.h was pulled
in via device.h -- but that is something we are going to make
go away soon.
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>

drivers/of/of_pci.c

 #include <linux/kernel.h>
+#include <linux/export.h>
 #include <linux/of.h>
 #include <linux/of_pci.h>
 #include <asm/prom.h>