[rust/coverage] Use new flag for coverage instrumentation

> warning: `-Z instrument-coverage` is deprecated; use `-C
instrument-coverage`

Test: above warning is absent when running:
    $ m CLANG_COVERAGE=true NATIVE_COVERAGE_PATHS=* rust
Change-Id: I8687c04534db3c8a67f209b93ed13d54c2f86dc8
diff --git a/rust/coverage_test.go b/rust/coverage_test.go
index f3cd375..0f599d7 100644
--- a/rust/coverage_test.go
+++ b/rust/coverage_test.go
@@ -56,7 +56,7 @@
 	fizzCov := ctx.ModuleForTests("fizz_cov", "android_arm64_armv8-a_cov").Rule("rustc")
 	buzzNoCov := ctx.ModuleForTests("buzzNoCov", "android_arm64_armv8-a").Rule("rustc")
 
-	rustcCoverageFlags := []string{"-Z instrument-coverage", " -g "}
+	rustcCoverageFlags := []string{"-C instrument-coverage", " -g "}
 	for _, flag := range rustcCoverageFlags {
 		missingErrorStr := "missing rustc flag '%s' for '%s' module with coverage enabled; rustcFlags: %#v"
 		containsErrorStr := "contains rustc flag '%s' for '%s' module with coverage disabled; rustcFlags: %#v"