change lora32_cfg_t pin types to int8_t and default to -1

include/esp32-lora.h

@@ -89,6 +89,15 @@
   .implicitHeader = false,\
   .useCRC = false,\
   .fifoIdx = 0,\
+  .copi = -1,\
+  .cipo = -1,\
+  .clk = -1,\
+  .dio0 = -1,\
+  .dio1 = -1,\
+  .dio2 = -1,\
+  .nss = -1,\
+  .reset = -1,\
+  .spi_host = 1,\
 }
 
 enum freq {
@@ -114,17 +123,17 @@ typedef struct {
 } lora32_handle_t;
 
 typedef struct lora32_cfg_t {
-  uint8_t nss;
-  uint8_t cipo;
-  uint8_t copi;
-  uint8_t clk;
-  uint8_t reset;
   uint8_t fifoIdx;
   uint8_t channel;
   uint8_t bandwidth;
   uint8_t spreadingFactor;
   uint8_t codingRate;
 
+  int8_t nss;
+  int8_t cipo;
+  int8_t copi;
+  int8_t clk;
+  int8_t reset;
   int8_t dio0;
   int8_t dio1;
   int8_t dio2;