Fixed return value in `_rmt_BeginMetalSample` declaration #125

Job	Run time
build-macos (linux, x64, release)	22s
build-linux (linux, x86)	19s
build-android (android, armv7, release, 21)	35s
build-linux (linux, x64)	24s
build-windows (windows, x86, debug, 14.3)	1m 6s
build-android (android, arm64, release, 21)	38s
build-windows (windows, x86, debug, 14.2)	1m 18s
build-windows (windows, x86, debug, 14.1)	1m 2s
build-windows (windows, x86, release, 14.3)	38s
build-windows (windows, x86, release, 14.2)	1m 17s
build-windows (windows, x86, release, 14.1)	58s
build-windows (windows, x64, debug, 14.3)	1m 24s
build-windows (windows, x64, debug, 14.2)	59s
build-windows (windows, x64, debug, 14.1)	47s
build-windows (windows, x64, release, 14.3)	1m 3s
build-windows (windows, x64, release, 14.2)	33s
build-windows (windows, x64, release, 14.1)	59s
	14m 22s

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