libfdt: Trivial cleanup for CHECK_HEADER)

Currently the CHECK_HEADER() macro is defined local to fdt_ro.c.
However, there are a handful of functions (fdt_move, rw_check_header,
fdt_open_into) from other files which could also use it (currently
they open-code something more-or-less identical).  Therefore, this
patch moves CHECK_HEADER() to libfdt_internal.h and uses it in those
places.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
diff --git a/libfdt/libfdt_internal.h b/libfdt/libfdt_internal.h
index 1e60936..52e1b8d 100644
--- a/libfdt/libfdt_internal.h
+++ b/libfdt/libfdt_internal.h
@@ -58,6 +58,13 @@
 #define memeq(p, q, n)	(memcmp((p), (q), (n)) == 0)
 #define streq(p, q)	(strcmp((p), (q)) == 0)
 
+#define CHECK_HEADER(fdt) \
+	{ \
+		int err; \
+		if ((err = fdt_check_header(fdt)) != 0) \
+			return err; \
+	}
+
 uint32_t _fdt_next_tag(const void *fdt, int startoffset, int *nextoffset);
 const char *_fdt_find_string(const char *strtab, int tabsize, const char *s);
 int _fdt_node_end_offset(void *fdt, int nodeoffset);