spi: dw: remove redundant assignment to variable len

spi: dw: remove redundant assignment to variable len

The variable id len being initialized with a value that is never read,
it is being re-assigned later on in a for-loop. The initialization is
redundant and can be removed.

Cleans up clang scan build warning:
drivers/spi/spi-dw-dma.c:580:17: warning: Although the value stored
to 'len' is used in the enclosing expression, the value is never
actually read from 'len' [deadcode.DeadStores]

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Acked-by: Serge Semin <fancer.lancer@gmail.com>
Link: https://msgid.link/r/20240215131603.2062332-1-colin.i.king@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>