p54spi: fix p54spi_tx_frame DMA transfer initiation and skb cleanup

p54spi_tx_frame wasn't waiting for HOST_ALLOWED in SPI_ADRS_DMA_WRITE_CTRL.
This resulted in frequent 'WR_READY timeout' on beacon resubmission.

Also don't free skb on error path, as it gets freed on p54spi_wq_tx.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Acked-by: Christian Lamparter <chunkeey@web.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>