ASoC: cygnus: remove redundant assignment to pointer 'res'

The pointer res is being initialized with a value that is never read
and re-assigned immediately after, hence the initialization is redundant
and can be removed.

Cleans up clang warning:
sound/soc/bcm/cygnus-ssp.c:1284:19: warning: Value stored to 'res'
during its initialization is never read

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Mark Brown <broonie@kernel.org>