iio: fix memory leak in iio_device_register_eventset()

iio: fix memory leak in iio_device_register_eventset()

When iio_device_register_sysfs_group() returns failed,
iio_device_register_eventset() needs to free attrs array.

Otherwise, kmemleak would scan & report memory leak as below:

unreferenced object 0xffff88810a1cc3c0 (size 32):
  comm "100-i2c-vcnl302", pid 728, jiffies 4295052307 (age 156.027s)
  backtrace:
    __kmalloc+0x46/0x1b0
    iio_device_register_eventset at drivers/iio/industrialio-event.c:541
    __iio_device_register at drivers/iio/industrialio-core.c:1959
    __devm_iio_device_register at drivers/iio/industrialio-core.c:2040

Fixes: 32f171724e5c ("iio: core: rework iio device group creation")
Signed-off-by: Zeng Heng <zengheng4@huawei.com>
Link: https://lore.kernel.org/r/20221115023712.3726854-1-zengheng4@huawei.com
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>