iio: pressure: dps310: Refactor startup procedure

Move the startup procedure into a function, and correct a missing
check on the return code for writing the PRS_CFG register.

Cc: <stable@vger.kernel.org>
Signed-off-by: Eddie James <eajames@linux.ibm.com>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20220915195719.136812-2-eajames@linux.ibm.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>