clk: clk-xgene: Add description for 'mask' and fix formatting for 'flags'

clk: clk-xgene: Add description for 'mask' and fix formatting for 'flags'

Fixes the following W=1 kernel build warning(s):

 drivers/clk/clk-xgene.c:229: warning: Function parameter or member 'mask' not described in 'xgene_clk_pmd'
 drivers/clk/clk-xgene.c:229: warning: Function parameter or member 'flags' not described in 'xgene_clk_pmd'

Cc: Michael Turquette <mturquette@baylibre.com>
Cc: Stephen Boyd <sboyd@kernel.org>
Cc: Loc Ho <lho@apm.com>
Cc: linux-clk@vger.kernel.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20210126124540.3320214-18-lee.jones@linaro.org
Signed-off-by: Stephen Boyd <sboyd@kernel.org>