minor cleanups, improve error handling

gracefully handle UFS_BSG not being enabled in the kernel, rather than
putting the device into a semi-bricked state (oops).

bootctrl_impl.cpp

@@ -33,6 +33,7 @@
 
 #include "utils.h"
 #include "gpt-utils.h"
+#include "ufs-bsg.h"
 
 #include "bootctrl.h"
 
@@ -607,6 +608,10 @@ int set_active_boot_slot(unsigned slot)
 		goto error;
 	}
 
+	if (ufs_bsg_dev_open() < 0) {
+		goto error;
+	}
+
 	//The partition list just contains prefixes(without the _a/_b) of the
 	//partitions that support A/B. In order to get the layout we need the
 	//actual names. To do this we append the slot suffix to every member