iwlwifi: yoyo: don't access TLV before verifying len

If we access the TLV memory with shorter len than the struct
we access garbage data that was not given by the user.

On the way rewrite the checker in a cleaner way.

Signed-off-by: Mordechay Goodstein <mordechay.goodstein@intel.com>
Fixes: a9248de4 ("iwlwifi: dbg_ini: add TLV allocation new API support")
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20200424182644.54418c829390.I15d6b462a0e69a280b6c6cfbcb6bcb05bb5f79ee@changeid