drm/i915/display/adl_p: Drop earlier return in tc_has_modular_fia()

MODULAR_FIA_MASK is set in adl_p so we can drop this ealier return
and read registers.
Also to avoid warnings from icl_tc_port_assert_ref_held() when
calling tc_cold_block() in this functions it is necessary to held the
lock.

Cc: Imre Deak <imre.deak@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Reviewed-by: Clint Taylor <Clinton.A.Taylor@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210524214805.259692-1-jose.souza@intel.com