libie: prevent memleak in fwlog code

All cmd_buf buffers are allocated and need to be freed after usage.
Add an error unwinding path that properly frees these buffers.

The memory leak happens whenever fwlog configuration is changed. For
example:

$echo 256K > /sys/kernel/debug/ixgbe/0000\:32\:00.0/fwlog/log_size

Fixes: 96a9a9341cda ("ice: configure FW logging")
Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Signed-off-by: Michal Swiatkowski <michal.swiatkowski@linux.intel.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Tested-by: Rinitha S <sx.rinitha@intel.com> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>