dca: Use PTR_ERR_OR_ZERO() to simplify code

The function PTR_ERR_OR_ZERO() contains the check of
IS_ERR() and the return of PTR_ERR() or zero.

Signed-off-by: Zhang Shengju <zhangshengju@cmss.chinamobile.com>
Signed-off-by: Tang Bin <tangbin@cmss.chinamobile.com>
Link: https://lore.kernel.org/r/20200507111224.4176-1-tangbin@cmss.chinamobile.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>