clk: test: add missing MODULE_DESCRIPTION() macros

make allmodconfig && make W=1 C=1 reports:
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/clk/clk_test.o
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/clk/clk-gate_test.o
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/clk/clk-fractional-divider_test.o

Add the missing invocations of the MODULE_DESCRIPTION() macro.

Signed-off-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Link: https://lore.kernel.org/r/20240602-md-clk-test-v1-1-a6afd4793337@quicinc.com


[sboyd@kernel.org: Reword header and description]
Signed-off-by: Stephen Boyd <sboyd@kernel.org>