cxgb4: no need to check return value of debugfs_create functions

When calling debugfs functions, there is no need to ever check the
return value.  The function can work or not, but the code logic should
never do something different based on this.

If a debugfs call fails, it will properly warn in the syslog, there's no
need for all individual drivers to also print a message, so that is one
more reason to not care about checking the return values.

Cc: Vishal Kulkarni <vishal@chelsio.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Casey Leedom <leedom@chelsio.com>
Cc: netdev@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>