iio: adc: ade9000: remove unused ADE9000_ST_ERROR macro

The ADE9000_ST_ERROR macro references ADE9000_ST1_ERROR0
through ADE9000_ST1_ERROR3, but the actual defined symbols
use the BIT suffix. Since this macro is currently unused
in the driver, remove it entirely rather than fixing the names.
It can be reintroduced in a future patch when it is actually needed.

The individual error bit definitions (bits 28-31 of the STATUS1
register at 0x403) are retained as they follow the convention of
defining all register fields.

Reference: ADE9000 datasheet (Rev. B, Page 61), STATUS1 register
(0x403), bits 28-31 define ERROR0 through ERROR3 status flags.

Suggested-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Signed-off-by: Giorgi Tchankvetadze <giorgitchankvetadze1997@gmail.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>