clk: sprd: check its parent status before reading gate clock

clk: sprd: check its parent status before reading gate clock

Some clocks only can be accessed if their parent is enabled. mipi_csi_xx
clocks on SC9863A are an examples. We have to ensure the parent clock is
enabled when reading those clocks.

Signed-off-by: Chunyan Zhang <chunyan.zhang@unisoc.com>
Link: https://lkml.kernel.org/r/20200527053638.31439-2-zhang.lyra@gmail.com
Signed-off-by: Stephen Boyd <sboyd@kernel.org>