xhci: dbc: Fix memory leak in xhci_alloc_dbc()

xhci: dbc: Fix memory leak in xhci_alloc_dbc()

If DbC is already in use, then the allocated memory for the xhci_dbc struct
doesn't get freed before returning NULL, which leads to a memleak.

Fixes: 534675942e90 ("xhci: dbc: refactor xhci_dbc_init()")
Cc: stable@vger.kernel.org
Signed-off-by: Rafael Mendonca <rafaelmendsr@gmail.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20220921123450.671459-3-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>