ALSA: es18xx: Remove the unneeded result variable

Return the value inb() directly instead of storing it in another redundant
 variable.

Reported-by: Zeal Robot <zealci@zte.com.cn>
Signed-off-by: ye xingchen <ye.xingchen@zte.com.cn>
Link: https://lore.kernel.org/r/20220920064605.215318-1-ye.xingchen@zte.com.cn
Signed-off-by: Takashi Iwai <tiwai@suse.de>