soc: amlogic: meson-clk-measure: protect measure with a mutex

soc: amlogic: meson-clk-measure: protect measure with a mutex

[ Upstream commit 3a760d986568b67d1f8411dab64608075817b90d ]

In order to protect clock measuring when multiple process asks for
a measure, protect the main measure function with mutexes.

Reviewed-by: Kevin Hilman <khilman@baylibre.com>
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>