Revert "fix(SubGhz): SPISettings not properly defined"

This reverts commit d61ad83.

Author: fpistm

Diff for: libraries/SubGhz/src/SubGhz.cpp

@@ -21,6 +21,8 @@ extern "C" void SUBGHZ_Radio_IRQHandler(void)
   SubGhz.handleIrq();
 }
 
+constexpr SPISettings SubGhzClass::spi_settings;
+
 void SubGhzClass::handleIrq()
 {
   if (callback) {

Diff for: libraries/SubGhz/src/SubGhz.h

@@ -101,7 +101,7 @@ class SubGhzClass {
     // supported by the radio, which should always work (no chance of
     // bad wiring that requires reducing the speed).
     // This value should be passed to `SubGhz.SPI.beginTransaction()`.
-    const SPISettings spi_settings = {16000000, MSBFIRST, SPI_MODE0};
+    static constexpr SPISettings spi_settings = {16000000, MSBFIRST, SPI_MODE0};
 
   protected:
     // To access handleIrq()