ice: Fix a couple NULL vs IS_ERR() bugs

ice: Fix a couple NULL vs IS_ERR() bugs

The ice_repr_create() function returns error pointers.  It never returns
NULL.  Fix the callers to check for IS_ERR().

Fixes: 977514fb0fa8 ("ice: create port representor for SF")
Fixes: 415db8399d06 ("ice: make representor code generic")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/7f7aeb91-8771-47b8-9275-9d9f64f947dd@stanley.mountain
Signed-off-by: Jakub Kicinski <kuba@kernel.org>