iwlwifi: mvm: rs: don't override the rate history in the search cycle

When we are in a search cycle, we try different combinations
of parameters. Those combinations are called 'columns'.
When we switch to a new column, we first need to check if
this column has a suitable rate, if not, we can't try it.
This means we must not erase the statistics we gathered
for the previous column until we are sure that we are
indeed switching column.

The code that tries to switch to a new column first sets
a whole bunch of things for the new column, and only then
checks that we can find suitable rates in that column.
While doing that, the code mistakenly erased the rate
statistics. This code was right until
struct iwl_scale_tbl_info grew up for TPC.

Fix this to make sure we don't erase the rate statistics
until we are sure that we can indeed switch to the new
column.

Note that this bug is really harmless since it causes a
change in the behavior only when we can't find any rate
in the new column which should really not happen. In the
case we do find a suitable we reset the rate statistics
a few lines later anyway.

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>