staging: clocking-wizard: prefer 'help' in Kconfig

Fixes the checkpatch warning:

WARNING: prefer 'help' over '---help---' for new help texts
+config COMMON_CLK_XLNX_CLKWZRD

Signed-off-by: Kyle Buzby <kyle.buzby@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>