tcan4x5x: Fix various issues

Fix a kernel panic where zeroing out the memory
over ran the buffer allocation.

Add the transmission complete interrupt to signify
that the FIFO was transmitted.

Removed dedicated buffers in the setup so the device
uses FIFOs.

Removed writing to the reserved bit in the Tx header.

Change-Id: I14a4834f0718bc7b2246d05b6cddc7c862a5902c
Signed-off-by: Dan Murphy <dmurphy@ti.com>
Git-repo: https://git.ti.com/cgit/ti-analog-linux-kernel/dmurphy-analog/log/?h=tcan4x5x_upstream


Git-commit: 9cd7a900
Signed-off-by: Zhenlin Lian <lianzhenlin@codeaurora.org>