mfd: Fix missing stmpe kerneldoc

Generating kerneldoc for STMPE result in warnings, so fix this by
adding missing documentation.

Signed-off-by: Om Prakash <omprakash.pal@stericsson.com>
Reviewed-by: Rabin Vincent <rabin.vincent@stericsson.com>
Reviewed-by: Jonas Aberg <jonas.aberg@stericsson.com>
Reviewed-by: Srinidhi Kasagar <srinidhi.kasagar@stericsson.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
diff --git a/drivers/mfd/stmpe.h b/drivers/mfd/stmpe.h
index 0dbdc4e..e4ee3895 100644
--- a/drivers/mfd/stmpe.h
+++ b/drivers/mfd/stmpe.h
@@ -42,6 +42,7 @@
  * @id_mask:	bits valid in CHIPID register for comparison with id_val
  * @num_gpios:	number of GPIOS
  * @af_bits:	number of bits used to specify the alternate function
+ * @regs: variant specific registers.
  * @blocks:	list of blocks present on this device
  * @num_blocks:	number of blocks present on this device
  * @num_irqs:	number of internal IRQs available on this device