wigig_sensing: make equal sized SPI transactions

This optimization reads the data over SPI in a single burst size
transaction, or in multiple equal sized transactions. The equal size
prevents reprogramming of the SPI length register.

Change-Id: Ie1cfa73aa72a796ab7af5c1d9151dbce8414de58
Signed-off-by: Gidon Studinski <gidons@codeaurora.org>