mmc: core: Provide description for sdio_set_host_pm_flags()'s 'flag' arg

Add missing kerneldoc entry for sdio_set_host_pm_flags()'s 'flag'
function argument.

Fixes the following W=1 kernel build warning:

 kernel/drivers/mmc/core/sdio_io.c:722: warning: Function parameter or member 'flags' not described in 'sdio_set_host_pm_flags'

Cc: Pierre Ossman <drzeus@drzeus.cx>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20200701124702.908713-3-lee.jones@linaro.orgSigned-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/core/sdio_io.c

@@ -709,6 +709,7 @@ EXPORT_SYMBOL_GPL(sdio_get_host_pm_caps);
 /**
  *	sdio_set_host_pm_flags - set wanted host power management capabilities
  *	@func: SDIO function attached to host
+ *	@flags: Power Management flags to set
  *
  *	Set a capability bitmask corresponding to wanted host controller
  *	power management features for the upcoming suspend state.