eeprom: idt_89hpesx: clean up an error pointer vs NULL inconsistency

We check for IS_ERR_OR_NULL() here, but later we check the same thing
for NULL only.  It turns out that it can only be NULL so we can make the
checking consistent by removing the ERR_PTR stuff.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>