IB/iser: remove uninitialized variable len

The variable len is not being inintialized and the uninitialized value is
being returned. However, this return path is never reached because the
default case in the switch statement returns -ENOSYS.  Clean up the code
by replacing the return -ENOSYS with a break for the default case and
returning -ENOSYS at the end of the function.  This allows len to be
removed.  Also remove redundant break that follows a return statement.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Max Gurtovoy <maxg@mellanox.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>