Fix broken compilation. As CBFS is now enabled by default,
CONFIG_FALLBACK_SIZE should be equal to CONFIG_ROM_IMAGE_SIZE and not
CONFIG_ROM_SIZE

Signed-off-by: Arnaud Maye <arnaud.maye@4dsp.com>


Index: intel/truxton/Config.lb
===================================================================
--- intel/truxton/Config.lb	(revision 4604)
+++ intel/truxton/Config.lb	(working copy)
@@ -30,7 +30,7 @@
 
 ## CONFIG_FALLBACK_SIZE is the amount of the ROM the complete fallback image
 ## (including payload) will use
-option CONFIG_FALLBACK_SIZE = CONFIG_ROM_SIZE
+option CONFIG_FALLBACK_SIZE = CONFIG_ROM_IMAGE_SIZE
 
 romimage "fallback"
 	option CONFIG_USE_FALLBACK_IMAGE=1
