Fixed rxwm setting as it defines the maximum number of received bytes

*before* the interrupt

riscv-bldc-forced-commutation/src/io/spi.h

@@ -169,7 +169,7 @@ public:
     template<size_t SIZE>
     static bool transfer(std::array<uint8_t, SIZE>& bytes){
         csmode_reg().mode=2; // HOLD mode
-        rxctrl_reg().rxmark=bytes.size(); // trigger irq if 3 bytes are received;
+        rxctrl_reg().rxmark=bytes.size()-1; // trigger irq if more than 2 bytes are received;
         ie_reg().rxwm=1;
         // write data bytes
         for(size_t i=0; i<bytes.size(); ++i)