kdump-lib.sh: fix a warning in prepare_kdump_bootinfo()
    
    Resolves: bz1968374
    Upstream: Fedora
    Conflict: None
    
    commit 39a642b66b2b4341a1345b63c5731e4ab90ad1b5
    Author: Hari Bathini <hbathini@linux.ibm.com>
    Date:   Tue Jun 1 16:46:58 2021 +0530
    
        kdump-lib.sh: fix a warning in prepare_kdump_bootinfo()
    
        Fix the warning observed when KDUMP_KERNELVER is specified:
    
          kdumpctl[10926]: /lib/kdump/kdump-lib.sh: line 697: [: missing `]'
    
        Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
        Acked-by: Kairui Song <kasong@redhat.com>
    
    Signed-off-by: Pingfan Liu <piliu@redhat.com>