fix: goroutine leak when timeout

[andyzhangx]

What type of PR is this?
/kind bug

What this PR does / why we need it:
fix: goroutine leak

The write operation to a channel in Go is blocking unless there is a receiver waiting for it, this means after WaitUntilTimeout exit, the goroutine will remain stuck at done <- true forever.
After changed to buffered channel, even if there is no receiver, done <- true can successfully write and continue.

Which issue(s) this PR fixes:

Fixes #

Requirements:

• uses conventional commit messages
• includes documentation
• adds unit tests
• tested upgrade from previous version

Special notes for your reviewer:

~/go/src/github.com/kubernetes-csi/csi-driver-smb/pkg/util# go test
--- FAIL: TestWaitUntilTimeout (3.44s)
    util_test.go:80: found unexpected goroutines:
        [Goroutine 8 in state chan send, with github.com/kubernetes-csi/csi-driver-smb/pkg/util.WaitUntilTimeout.func1 on top of the stack:
        github.com/kubernetes-csi/csi-driver-smb/pkg/util.WaitUntilTimeout.func1()
                /root/go/src/github.com/kubernetes-csi/csi-driver-smb/pkg/util/util.go:48 +0x65
        created by github.com/kubernetes-csi/csi-driver-smb/pkg/util.WaitUntilTimeout in goroutine 6
                /root/go/src/github.com/kubernetes-csi/csi-driver-smb/pkg/util/util.go:46 +0xb3
        ]
FAIL

Release note:

fix: goroutine leak

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: andyzhangx

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• OWNERS [andyzhangx]

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[coveralls]

Pull Request Test Coverage Report for Build 14768627236

Details

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 78.178%

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Totals
Change from base Build 14666256795:	0.0%
Covered Lines:	1107
Relevant Lines:	1416

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💛 - Coveralls