staging: isdn: remove unnecessary parentheses

Fix the following checkpatch error:

ERROR: return is not a function, parentheses are not required
FILE: drivers/staging/isdn/hysdn/hysdn_net.c:289:
+        return (0);                /* and return success */

Signed-off-by: Thiago Bonotto <thbonotto@gmail.com>
Link: https://lore.kernel.org/r/20190802202323.27117-1-thbonotto@gmail.com


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