staging: iio: replace clk_get() with devm_clk_get()

This patch replaces the clk_get() with devm_clk_get().Accordingly,modified
the error paths,rename error labels and removed clk_put() in probe() &
remove functions.

Signed-off-by: Hari Prasath Gujulan Elango <hgujulan@visteon.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>