fixed i2c_simple compile error, added doc in the header

firmware/slavechip/i2c_simple.c

@@ -96,7 +96,7 @@ uint8_t i2c_write_i(uint8_t addr, uint8_t len, uint8_t *data, uint8_t stop)
 
 inline uint8_t i2c_write(uint8_t addr, uint8_t len, uint8_t *data)
 {
-	return i2c_write(addr, len, data, 1);
+	return i2c_write_i(addr, len, data, 1);
 }
 
 uint8_t i2c_write_read(uint8_t addr, uint8_t writelen, uint8_t *writedata, uint8_t readlen, uint8_t *readdata)

firmware/slavechip/i2c_simple.h

@@ -13,6 +13,7 @@ uint8_t i2c_read(uint8_t addr, uint8_t len, uint8_t *data);
 uint8_t i2c_write(uint8_t addr, uint8_t len, uint8_t *data);
 
 /* writes, followed by a repeated start and a read */
+/* returns the number of bytes read. if 0 is returned the write might have failed */
 uint8_t i2c_write_read(uint8_t addr, uint8_t writelen, uint8_t *writedata, uint8_t readlen, uint8_t *readdata);
 
 #endif