Fix slashes in SPI library

Author: igrr

hardware/esp8266com/esp8266/libraries/SPI/HSPI.cpp

@@ -1,5 +1,5 @@
-#include "include\HSPI.h"
-#include "include\spi_register.h"
+#include "include/HSPI.h"
+#include "include/spi_register.h"
 
 #define __min(a,b) ((a > b) ? (b):(a))
 

hardware/esp8266com/esp8266/libraries/SPI/SPI.cpp

@@ -11,7 +11,7 @@
  */
 
 #include "SPI.h"
-#include "include\HSPI.h"
+#include "include/HSPI.h"
 
 SPIClass SPI;