spi: pxa2xx-pci: Balance reference count for PCI DMA device

The pci_get_slot() increases its reference count, the caller
must decrement the reference count by calling pci_dev_put().

Fixes: 743485ea ("spi: pxa2xx-pci: Do a specific setup in a separate function")
Fixes: 25014521 ("spi: pxa2xx-pci: Enable DMA for Intel Merrifield")
Reported-by: Wang Qing <wangqing@vivo.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20220223191637.31147-1-andriy.shevchenko@linux.intel.com


Signed-off-by: Mark Brown <broonie@kernel.org>