clk: renesas: r9a06g032: Fix kerneldoc warning

Mention the 'dual' structure in the kdoc.  This fixes the following
W=1 warning during build:

> drivers/clk/renesas/r9a06g032-clocks.c:119: warning: Function parameter or member 'dual' not described in 'r9a06g032_clkdesc'

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202309101314.kTRoxND5-lkp@intel.com/
Signed-off-by: Ralph Siemsen <ralph.siemsen@linaro.org>
Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20230913203805.465780-1-ralph.siemsen@linaro.org
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>

Author: rfs613

drivers/clk/renesas/r9a06g032-clocks.c

@@ -109,6 +109,7 @@ enum gate_type {
  *             must be in ascending order, zero for unused
  * @div:       divisor for fixed-factor clock
  * @mul:       multiplier for fixed-factor clock
+ * @dual:      substructure for dual clock gates
  * @group:     UART group, 0=UART0/1/2, 1=UART3/4/5/6/7
  * @sel:       select either g1/r1 or g2/r2 as clock source
  * @g1:        1st source gate (clock enable/disable)