gpio: gpio-syscon: Fix formatting issues which confuse kerneldoc

Kerneldoc expects struct properties to be documented using the syntax
'@.*: ', but no '@' has been provided in 'struct syscon_gpio_data's
header.  Add them to stop confusing kerneldoc.

Fixes the following W=1 warnings:

 drivers/gpio/gpio-syscon.c:48: warning: Function parameter or member 'compatible' not described in 'syscon_gpio_data'
 drivers/gpio/gpio-syscon.c:48: warning: Function parameter or member 'flags' not described in 'syscon_gpio_data'
 drivers/gpio/gpio-syscon.c:48: warning: Function parameter or member 'bit_count' not described in 'syscon_gpio_data'
 drivers/gpio/gpio-syscon.c:48: warning: Function parameter or member 'dat_bit_offset' not described in 'syscon_gpio_data'
 drivers/gpio/gpio-syscon.c:48: warning: Function parameter or member 'dir_bit_offset' not described in 'syscon_gpio_data'
 drivers/gpio/gpio-syscon.c:48: warning: Function parameter or member 'set' not described in 'syscon_gpio_data'
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Cc: Alexander Shiyan <shc_work@mail.ru>
Link: https://lore.kernel.org/r/20200630133345.2232932-7-lee.jones@linaro.orgSigned-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpio-syscon.c

@@ -24,16 +24,16 @@
 
 /**
  * struct syscon_gpio_data - Configuration for the device.
- * compatible:		SYSCON driver compatible string.
- * flags:		Set of GPIO_SYSCON_FEAT_ flags:
+ * @compatible:		SYSCON driver compatible string.
+ * @flags:		Set of GPIO_SYSCON_FEAT_ flags:
  *			GPIO_SYSCON_FEAT_IN:	GPIOs supports input,
  *			GPIO_SYSCON_FEAT_OUT:	GPIOs supports output,
  *			GPIO_SYSCON_FEAT_DIR:	GPIOs supports switch direction.
- * bit_count:		Number of bits used as GPIOs.
- * dat_bit_offset:	Offset (in bits) to the first GPIO bit.
- * dir_bit_offset:	Optional offset (in bits) to the first bit to switch
+ * @bit_count:		Number of bits used as GPIOs.
+ * @dat_bit_offset:	Offset (in bits) to the first GPIO bit.
+ * @dir_bit_offset:	Optional offset (in bits) to the first bit to switch
  *			GPIO direction (Used with GPIO_SYSCON_FEAT_DIR flag).
- * set:		HW specific callback to assigns output value
+ * @set:		HW specific callback to assigns output value
  *			for signal "offset"
  */