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>