fix compiler warnings

[andybrown668]

Hi, thanks for the lib - works great!
here's a patch to get rid of compiler warnings - I see these when cross-compiling to arm with
CC=arm-linux-gnueabi-gcc CGO_ENABLED=1 GOOS=linux GOARCH=arm GOARM=6 go build <app.go>

----------------------------------- dht.go.h -----------------------------------
index 6cda1e0..fc05c70 100644
@@ -7,6 +7,7 @@
#include <fcntl.h>
#include <sched.h>
#include <time.h>
+#include <unistd.h>

// GPIO direction: receive either output data to specific GPIO pin.
#define IN 0
@@ -52,7 +53,9 @@ static int gpio_export(int port, Pin *pin) {
}
(*pin).pin = port;
bytes_written = snprintf(buffer, BUFFER_MAX, "%d", (*pin).pin);

• write(fd, buffer, bytes_written);

• if (-1 == write(fd, buffer, bytes_written)){

•    fprintf(stderr, "Failed to export pin!\n");
  

• }
  close(fd);

  #define DIRECTION_MAX 35
  @@ -92,7 +95,9 @@ static int gpio_unexport(Pin *pin) {
  }

  bytes_written = snprintf(buffer, BUFFER_MAX, "%d", (*pin).pin);

• write(fd, buffer, bytes_written);

• if (-1 == write(fd, buffer, bytes_written)){

•    fprintf(stderr, "Failed to unexport pin!\n");
  

• }
  close(fd);
  return 0;
  }

[d2r2]

Hi, @andybrown668! Thank you for pleasant words regarding this lib :)
Give me few days and I will come back with extended answer.
Frankly, I never try to cross comply this lib (and made all this stuff few years ago), so give me some time to reproduce this issue, with the approach you describe.

[d2r2]

@andybrown668, thanks again for pointing issue in C-code! Your changes proposed merged to the library.