mfd: tps65218: Repair incorrect function argument name 's/tps65218/tps/'

The kerneldocs for both tps65218_reg_write() and tps65218_update_bits()
describe their first arguments as 'tps65218', when in reality these are
simply called 'tps'.

Fixes the following W=1 warnings:

 drivers/mfd/tps65218.c:58: warning: Function parameter or member 'tps' not described in 'tps65218_reg_write'
 drivers/mfd/tps65218.c:58: warning: Excess function parameter 'tps65218' description in 'tps65218_reg_write'
 drivers/mfd/tps65218.c:90: warning: Function parameter or member 'tps' not described in 'tps65218_update_bits'
 drivers/mfd/tps65218.c:90: warning: Excess function parameter 'tps65218' description in 'tps65218_update_bits'

Cc: Tony Lindgren <tony@atomide.com>
Cc: J Keerthy <j-keerthy@ti.com>
Cc: linux-omap@vger.kernel.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/mfd/tps65218.c

@@ -48,7 +48,7 @@ static const struct mfd_cell tps65218_cells[] = {
 /**
  * tps65218_reg_write: Write a single tps65218 register.
  *
- * @tps65218: Device to write to.
+ * @tps: Device to write to.
  * @reg: Register to write to.
  * @val: Value to write.
  * @level: Password protected level
@@ -79,7 +79,7 @@ EXPORT_SYMBOL_GPL(tps65218_reg_write);
 /**
  * tps65218_update_bits: Modify bits w.r.t mask, val and level.
  *
- * @tps65218: Device to write to.
+ * @tps: Device to write to.
  * @reg: Register to read-write to.
  * @mask: Mask.
  * @val: Value to write.