thunderbolt: Set variable tmu_params storage class specifier to static

smatch reports
drivers/thunderbolt/tmu.c:30:3: warning: symbol
  'tmu_params' was not declared. Should it be static?

This variable is only used in its defining file so should be static.
Signed-off-by: Tom Rix <trix@redhat.com>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>

drivers/thunderbolt/tmu.c

@@ -19,7 +19,7 @@ static const unsigned int tmu_rates[] = {
 	[TB_SWITCH_TMU_MODE_MEDRES_ENHANCED_UNI] = 16,
 };
 
-const struct {
+static const struct {
 	unsigned int freq_meas_window;
 	unsigned int avg_const;
 	unsigned int delta_avg_const;