i2c: iop3xx: Fix memory leak in probe error path

When handling devm_gpiod_get_optional() errors, free the memory already
allocated.  This fixes Smatch warnings:

    drivers/i2c/busses/i2c-iop3xx.c:437 iop3xx_i2c_probe() warn: possible memory leak of 'new_adapter'
    drivers/i2c/busses/i2c-iop3xx.c:442 iop3xx_i2c_probe() warn: possible memory leak of 'new_adapter'

Fixes: fdb7e884

 ("i2c: iop: Use GPIO descriptors")
Reported-by: kbuild test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>