staging: pi433: Rename struct pi433_device buffer field to tx_buffer.

Driver holds buffers in different structs, as does the HW.
Using explicit names for buffers increases readability.

Signed-off-by: Shahar Avidar <ikobh7@gmail.com>
Reviewed-by: Dan Carpenter <dan.carpenter@linaro.org>
Link: https://lore.kernel.org/r/20240405074000.3481217-2-ikobh7@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>