staging: iio: ad2s1210: remove redundant assignment to variable negative

staging: iio: ad2s1210: remove redundant assignment to variable negative

Variable negative is being assigned a value that is never read, it is
being re-assigned later. The assignment is redundant and can be removed.

Cleans up clang scan build warning:
drivers/staging/iio/resolver/ad2s1210.c:502:3: warning: Value stored
to 'negative' is never read [deadcode.DeadStores]

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Link: https://lore.kernel.org/r/20220418134603.81336-1-colin.i.king@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>