libfdt: fdt_create_with_flags(): Fix comparison warning

With -Wsign-compare, compilers warn about a mismatching signedness
in a comparison in fdt_create_with_flags().

By making hdrsize a signed integer (we are sure it's a very small
number), we avoid all the casts and have matching types.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Message-Id: <20201001164630.4980-4-andre.przywara@arm.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

libfdt/fdt_sw.c

@@ -108,7 +108,7 @@ static void *fdt_grab_space_(void *fdt, size_t len)
 
 int fdt_create_with_flags(void *buf, int bufsize, uint32_t flags)
 {
-	const size_t hdrsize = FDT_ALIGN(sizeof(struct fdt_header),
+	const int hdrsize = FDT_ALIGN(sizeof(struct fdt_header),
 				      sizeof(struct fdt_reserve_entry));
 	void *fdt = buf;