iwlwifi: mvm: demote non-compliant kernel-doc header

Fixes the following W=1 kernel build warning:

 drivers/net/wireless/intel/iwlwifi/mvm/rfi.c:11: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst

Cc: Stanislav Yakovlev <stas.yakovlev@gmail.com>
Signed-off-by: Yang Shen <shenyang39@huawei.com>
[removed the static const fix, since it's already done and
  updated the commit message accordingly.]
Link: https://lore.kernel.org/r/20210517050141.61488-7-shenyang39@huawei.comSigned-off-by: Luca Coelho <luciano.coelho@intel.com>

drivers/net/wireless/intel/iwlwifi/mvm/rfi.c

@@ -7,7 +7,7 @@
 #include "fw/api/commands.h"
 #include "fw/api/phy-ctxt.h"
 
-/**
+/*
  * DDR needs frequency in units of 16.666MHz, so provide FW with the
  * frequency values in the adjusted format.
  */