tcan4x5x: Fix rx FIFO handling

Fix #define for RX address offset
Fix #define for FIFO Rx start address
Change the index from regmap_update_bit to
regmap_write

Change-Id: I222d1f666f9b2429c6d9a23b6db4ff6f31adebb5
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: 72e5a0b6
Signed-off-by: Zhenlin Lian <lianzhenlin@codeaurora.org>