libflashrom.h: Add missing includes

<stddef.h> for `size_t` and <sys/types.h> for `off_t`.

Change-Id: Ifc84dfe2a06633321d0abd364bdea1216925a779
Signed-off-by: Nico Huber <nico.huber@secunet.com>
Reviewed-on: https://review.coreboot.org/c/30153
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: David Hendricks <david.hendricks@gmail.com>
diff --git a/libflashrom.h b/libflashrom.h
index 4fbcd35..38c95d2 100644
--- a/libflashrom.h
+++ b/libflashrom.h
@@ -18,6 +18,8 @@
 #ifndef __LIBFLASHROM_H__
 #define __LIBFLASHROM_H__ 1
 
+#include <sys/types.h>
+#include <stddef.h>
 #include <stdarg.h>
 
 int flashrom_init(int perform_selfcheck);