regulator: rpm-smd-regulator: Correct the get_optimum_mode function

Do not set the "CURRENT" KVP param in the "get_optimum_mode" function.
Because of this, when the consumers call the "regulator_set_load"
function the set_mode callback which actually sends the "CURRENT"
KVP to RPM subsystem is not getting invoked. Hence, remove it from
get_optimum_mode function as the same KVP is set in the the set_mode
callback.

Change-Id: I3d0a7c37a78c844459d864d92c96e02e4362d160
Signed-off-by: Kiran Gunda <kgunda@codeaurora.org>