staging: greybus: audio: fix uninitialized value issue

The current implementation for gbcodec_mixer_dapm_ctl_put() uses
uninitialized gbvalue for comparison with updated value. This was found
using static analysis with coverity.

Uninitialized scalar variable (UNINIT)
11. uninit_use: Using uninitialized value
gbvalue.value.integer_value[0].
460        if (gbvalue.value.integer_value[0] != val) {

This patch fixes the issue with fetching the gbvalue before using it for
    comparision.

Fixes: 6339d232 ("greybus: audio: Add topology parser for GB codec")
Reported-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Vaibhav Agarwal <vaibhav.sr@gmail.com>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/bc4f29eb502ccf93cd2ffd98db0e319fa7d0f247.1597408126.git.vaibhav.sr@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>