Fix -Wtautological-constant-out-of-range-compare warning

system/core/trusty/gatekeeper/trusty_gatekeeper.cpp:158:31: error: result of comparison of constant 'ERROR_NOT_IMPLEMENTED' (-3) with expression of type 'gatekeeper_error_t' is always false [-Werror,-Wtautological-constant-out-of-range-compare]
  158 |     } else if (response.error == ERROR_NOT_IMPLEMENTED) {
      |                ~~~~~~~~~~~~~~ ^  ~~~~~~~~~~~~~~~~~~~~~

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Bug: 72331526
Test: presubmit
Flag: EXEMPT, code cleanup
Change-Id: Iff07402cde898fd8500270f9e21440b4093dea7e
1 file changed