Non-effective critical sections on SPI send/receive methods

[ankostis]

From my rough understanding of FreeRTOS, i believe that the critical-sections on CLink_SPI::receive() and CLink_SPI::send() methods are non-effective, because they exclusion-lock created inside the stack of each method, so it's impossible to share it with any other code;
maybe the original intention of the code for them lock to become an instance-member of the CLink_SPI::class, correct?

• https://github.com/stanleyhuangyc/Freematics/blob/28c82e18fa4e55ec9cb5fc0d092a189046310de6/libraries/FreematicsPlus/FreematicsPlus.cpp#L365-L413
• https://github.com/stanleyhuangyc/Freematics/blob/28c82e18fa4e55ec9cb5fc0d092a189046310de6/libraries/FreematicsPlus/FreematicsPlus.cpp#L439-L454