gpio-uclass.c: Fix comparison of unsigned expression warning

We declare that gpio_base (which is the base for counting gpios, not an
address) is unsigned.  Therefore the comparison with >= 0 is always
true.  As the desire is to allow for this base number to be 0, we can
just drop this check.  Reported by clang-3.8.

Cc: Simon Glass <sjg@chromium.org>
Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

drivers/gpio/gpio-uclass.c

@@ -68,7 +68,7 @@ int dm_gpio_lookup_name(const char *name, struct gpio_desc *desc)
 		if (numeric != -1) {
 			offset = numeric - uc_priv->gpio_base;
 			/* Allow GPIOs to be numbered from 0 */
-			if (offset >= 0 && offset < uc_priv->gpio_count)
+			if (offset < uc_priv->gpio_count)
 				break;
 		}