Avoid [MTLDevice sampleTimestamps] unless the extension is enabled

This callsite was missed in a previous CL:
https://dawn-review.googlesource.com/c/dawn/+/59041

Bug: chromium:1226078
Change-Id: I3829dc16a8ec3c7b7274bc6057030bdade598ade
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/61584
Reviewed-by: Austin Eng <enga@chromium.org>
Commit-Queue: Austin Eng <enga@chromium.org>

src/dawn_native/metal/DeviceMTL.mm

diff --git a/src/dawn_native/metal/DeviceMTL.mm b/src/dawn_native/metal/DeviceMTL.mm
index ad9ed48..17c6ba9 100644
--- a/src/dawn_native/metal/DeviceMTL.mm
+++ b/src/dawn_native/metal/DeviceMTL.mm
@@ -134,7 +134,7 @@
 
         DAWN_TRY(mCommandContext.PrepareNextCommandBuffer(*mCommandQueue));
 
-        if (GetAdapter()->GetSupportedExtensions().IsEnabled(Extension::TimestampQuery)) {
+        if (IsExtensionEnabled(Extension::TimestampQuery)) {
             // Make a best guess of timestamp period based on device vendor info, and converge it to
             // an accurate value by the following calculations.
             mTimestampPeriod =