Update esp_err.h

Update esp_err.h

Renamed the internal rc to __err_rc to avoid clashes with local variables.
This code would not do the expected thing with the original ESP_ERROR_CHECK macro:

esp_err_t my_func(esp_err_t x)
{
  assert(x == 23);
}

esp_err_t rc = 23; //some value that is important fo the user
ESP_ERROR_CHECK(my_func(rc));

The macro will expand to:
esp_err_t rc = (my_func(rc));

And the code will assert, as my_func will receive a random value - whatever is in the internal macro rc temp variable. This is due to the C weirdness of allowing this code:

int x = x; //x has a random value.