x86: Fix a compiler warning in arch/x86/lib/realmode.c

Ensure that the value being passed to a %d format specifier is of type
int.

Signed-off-by: Gabe Black <gabeblack@chromium.org>

arch/x86/lib/realmode.c

@@ -41,7 +41,7 @@ int realmode_setup(void)
 	if (realmode_size > (REALMODE_MAILBOX - (char *)REALMODE_BASE)) {
 		printf("realmode switch too large (%ld bytes, max is %d)\n",
 		       realmode_size,
-		       (REALMODE_MAILBOX - (char *)REALMODE_BASE));
+		       (int)(REALMODE_MAILBOX - (char *)REALMODE_BASE));
 		return -1;
 	}