mfd: db8500-prcmu: Fix multiple incorrectly documented function names

mfd: db8500-prcmu: Fix multiple incorrectly documented function names

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

 drivers/mfd/db8500-prcmu.c:624: warning: expecting prototype for prcmu_get_current_mode(). Prototype was for prcmu_get_xp70_current_state() instead
 drivers/mfd/db8500-prcmu.c:908: warning: expecting prototype for db8500_set_ape_opp(). Prototype was for db8500_prcmu_set_ape_opp() instead
 drivers/mfd/db8500-prcmu.c:2303: warning: expecting prototype for db8500_prcmu_reset_modem(). Prototype was for db8500_prcmu_modem_reset() instead

Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Lee Jones <lee.jones@linaro.org>
Cc: Kumar Sanghvi <kumar.sanghvi@stericsson.com>
Cc: Sundar Iyer <sundar.iyer@stericsson.com>
Cc: Mattias Nilsson <mattias.i.nilsson@stericsson.com>
Cc: linux-arm-kernel@lists.infradead.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>