sandbox: fix enum host_platform_flags description

`make htmldocs` reports

    ./include/sandbox_host.h:14: warning:
    cannot understand function prototype: 'enum host_platform_flags '

Align the description with Sphinx style.

Fixes: 93e9af685f ("test: bootdev: scan with a broken high-priority device")
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Denis Mukhin <dmukhin@ford.com>

include/sandbox_host.h

@@ -9,10 +9,12 @@
 #define __SANDBOX_HOST__
 
 /**
- * Device flags.
+ * enum host_platform_flags - device flags
+ *
  */
 enum host_platform_flags {
-	HOST_FLAG_BROKEN		= BIT(0), /** Simulate broken device */
+	/** @HOST_FLAG_BROKEN:	simulate broken device */
+	HOST_FLAG_BROKEN		= BIT(0),
 };
 
 /**