ctl: optimize a test for user-defined element set to older kernels

ctl: optimize a test for user-defined element set to older kernels

In Linux 4.0 or former, call of ioctl(2) with SNDRV_CTL_IOCTL_ELEM_ADD
doesn't fill all of identical information in an argument; i.e. numid.
With the kernel, a test of user-defined element set fails.

This commit fixes the bug. The 'numid' field in identical information
is always zero when adding an element set, therefore zero check has an
effect.

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>