iwlwifi: dbg_ini: fix bad dump size calculation

The driver initiates the size value with the size of the struct and then
adds the size of the data and checks if the size is zero so size can not
be equal to zero.

Solve this by getting the data size, check that it is not equal to zero
and only then add the struct size.

Signed-off-by: Shahar S Matityahu <shahar.s.matityahu@intel.com>
Fixes: 7a14c23d ("iwlwifi: dbg: dump data according to the new ini TLVs")
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>