net: lan966x: remove debugfs directory in probe() error path

A debugfs directory entry is create early during probe(). This entry is
not removed on error path leading to some "already present" issues in
case of EPROBE_DEFER.

Create this entry later in the probe() code to avoid the need to change
many 'return' in 'goto' and add the removal in the already present error
path.

Fixes: 94281484

 ("net: lan966x: Add VCAP debugFS support")
Cc: <stable@vger.kernel.org>
Signed-off-by: Herve Codina <herve.codina@bootlin.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>