iio: resolver: ad2s1210: notify trigger and clear state on fault read error

ad2s1210_trigger_handler() walks several scan-mask branches and uses
"goto error_ret" to land on the iio_trigger_notify_done() teardown at
the bottom of the function for every I/O error -- except the
MOD_CONFIG fault-register read, which uses a bare "return ret":

	if (st->fixed_mode == MOD_CONFIG) {
		unsigned int reg_val;

		ret = regmap_read(st->regmap, AD2S1210_REG_FAULT, &reg_val);
		if (ret < 0)
			return ret;
		...
	}

Two problems on that path:

  - the handler returns a negative errno where the prototype expects
    an irqreturn_t (IRQ_HANDLED / IRQ_NONE), so the caller in the
    IIO core sees a value outside the enum;
  - iio_trigger_notify_done() is skipped, leaving the trigger
    busy-flag set. A single transient SPI/regmap error on the fault
    read then wedges the trigger so subsequent samples are dropped
    until the consumer is detached.

Convert the error path to "goto error_ret" so the failure path goes
through the same notify_done() teardown as every other error in the
handler.

Fixes: f9b9ff95be ("iio: resolver: ad2s1210: add support for adi,fixed-mode")
Signed-off-by: Stepan Ionichev <sozdayvek@gmail.com>
Reviewed-by: David Lechner <dlechner@baylibre.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/resolver/ad2s1210.c

@@ -1334,7 +1334,7 @@ static irqreturn_t ad2s1210_trigger_handler(int irq, void *p)
 
 		ret = regmap_read(st->regmap, AD2S1210_REG_FAULT, &reg_val);
 		if (ret < 0)
-			return ret;
+			goto error_ret;
 
 		st->sample.fault = reg_val;
 	}