ALSA: ens137x: remove redundant variable result

Variable result is being assigned a value from a calculation
however the variable is never read, so this redundant variable
can be removed.

Cleans up clang warning: Value stored to 'result' is never read

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>