wifi: iwlwifi: dvm: fix -Wunused-const-variable gcc warning

Fix the following gcc 13.1 warning observed with W=1:

drivers/net/wireless/intel/iwlwifi/dvm/rs.c:207:39: warning:
‘iwl_rate_mcs’ defined but not used [-Wunused-const-variable=]

This table is actually used in 'rs_sta_dbgfs_scale_table_read()'
only if CONFIG_MAC80211_DEBUGFS is enabled, so the whole thing
may be moved close to its actual use.

Signed-off-by: Dmitry Antipov <dmantipov@yandex.ru>
Link: https://lore.kernel.org/r/20230619103900.300628-1-dmantipov@yandex.ru


Signed-off-by: Johannes Berg <johannes.berg@intel.com>