iio: filter: admv8818: Force initialization of SDO

iio: filter: admv8818: Force initialization of SDO

When a weak pull-up is present on the SDO line, regmap_update_bits fails
to write both the SOFTRESET and SDOACTIVE bits because it incorrectly
reads them as already set.

Since the soft reset disables the SDO line, performing a
read-modify-write operation on ADI_SPI_CONFIG_A to enable the SDO line
doesn't make sense. This change directly writes to the register instead
of using regmap_update_bits.

Fixes: f34fe888ad05 ("iio:filter:admv8818: add support for ADMV8818")
Signed-off-by: Sam Winchenbach <swinchenbach@arka.org>
Link: https://patch.msgid.link/SA1P110MB106904C961B0F3FAFFED74C0BCF5A@SA1P110MB1069.NAMP110.PROD.OUTLOOK.COM
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>