regulator: Remove redundant set_mode call in drms_uA_update

The regulator framework checks if the current mode is the same as the
one being requested inside of regulator_set_mode. However, when
DRMS changing is allowed, regulator_enable calls drms_uA_update.
This function does not check the value of get_mode before calling
set_mode.

Modify drms_uA_update so that set_mode is only called if the requested
mode is different from the current mode returned by get_mode.

Change-Id: Ifb4f3069cf946e8474565ee82508c1ff45b36543
Signed-off-by: David Collins <collinsd@codeaurora.org>