net: caif: remove ineffective check

The check of the return value of sock_register() is ineffective.
"if(!err)" seems to be a typo. It is better to propagate the error code
to the callers of caif_sktinit_module(). This patch removes the check
statment and directly returns the result of sock_register().

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=188751
Signed-off-by: Pan Bian <bianpan2016@163.com>
Signed-off-by: David S. Miller <davem@davemloft.net>