i2c: stm32f7: Use devm_clk_get_enabled()

Replace the pair of functions, devm_clk_get() and
clk_prepare_enable(), with a single function
devm_clk_get_enabled().

Signed-off-by: Andi Shyti <andi.shyti@kernel.org>
Acked-by: Alain Volmat <alain.volmat@foss.st.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>