shell/main_blksync.c: Fix leak of file descriptor

Coverity Id 1063887. File descriptor not freed on error path.

cpukit/libmisc/shell/main_blksync.c

@@ -58,6 +58,7 @@ static int rtems_shell_main_blksync(
 
   if (rtems_disk_fd_sync (fd) < 0) {
     fprintf( stderr, "%s: driver sync failed: %s\n", argv[0], strerror (errno));
+    close (fd);
     return 1;
   }