This patch fixes a "Kernel Memory fault" panic coming from access_invalidate()routine during domain deactivation.  The problem occurs only if there are any errors during the execution of the bs_bfs_get_info routine.

stack trace 1
-------------
crash> tf
 > 0 stop_secondary_cpu 
 1 panic 
 2 event_timeout 
 3 printf 
 4 panic 
 5 trap 
 6 _XentMM 
 7 access_invalidate 
 8 bfs_dealloc 
 9 dmn_dealloc 
 10 bs_bfdmn_deactivate 
 11 fs_fset_get_info 
 12 msfs_real_syscall 
 13 msfs_syscall 
 14 syscall 
 15 _Xsyscall 

stack trace 2
-------------
crash> tf
 0 boot 
 1 panic  
 2 trap 
 3 _XentMM 
 4 access_invalidate
 5 bfs_dealloc   
 6 dmn_dealloc   
 7 bs_bfdmn_deactivate 
 8 msfs_unmount      
 9 cfs_unmount 
 10 dounmount  
 11 cfs_do_unmount_accept 
 12 cms_handle_send_msg  
 13 cms_kgs_callback_thread  


