ALSA: es1688_lib: Deletion of an unnecessary check before the function call "release_and_free_resource"

The release_and_free_resource() function tests whether its argument is NULL
and then returns immediately. Thus the test around the call is not needed.

This issue was detected by using the Coccinelle software.
Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: Takashi Iwai <tiwai@suse.de>