mkimage: SEGFAULT with imximage on 64 bit systems

Running mkimage to generate an imximage produces a SEGFAULT
on 64 bit machines due to pointer arithmetic limited to 32 bit.

Signed-off-by: Stefano Babic <sbabic@denx.de>
Acked-by: Kim Phillips <kim.phillips@freescale.com>
diff --git a/tools/imximage.h b/tools/imximage.h
index c579f51..b4d926d 100644
--- a/tools/imximage.h
+++ b/tools/imximage.h
@@ -81,7 +81,7 @@
 	uint32_t app_code_barker;
 	uint32_t app_code_csf;
 	uint32_t dcd_ptr_ptr;
-	hab_rsa_public_key *super_root_key;
+	uint32_t super_root_key;
 	uint32_t dcd_ptr;
 	uint32_t app_dest_ptr;
 } flash_header_t;