resp_open_zone() always calls zbc_open_zone() with parameter explicit set
to true.

If zbc_open_zone() is called with parameter explicit set to true, and the
current zone state is implicit open, it will call zbc_close_zone() on the
zone before proceeding.

Therefore, there is no need for resp_open_zone() to call zbc_close_zone()
on an implicitly open zone before calling zbc_open_zone().

Remove superfluous close zone in resp_open_zone().

Link: https://lore.kernel.org/r/20200821130007.39938-1-niklas.cassel@wdc.comReviewed-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Niklas Cassel <niklas.cassel@wdc.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>