iio: fix memory leak in iio_device_register_eventset()

In the Linux kernel, the following vulnerability has been resolved: 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