msm: clock-rpm: Remove last_set_khz/last_set_sleep_khz from rpm clk

Since last_set_khz and last_set_sleep_khz can be computed from the rate
value stored in the struct clk, remove them from rpm clk struct to avoid
unnecessary duplication.

By removing the duplication of data, this also fixes the issue caused by
clk.rate not matching last_set_khz/last_set_sleep_khz after a handoff.
The mismatch that occurs without this patch causes the call to
clk_set_rate() to return early without sending a new request to RPM when
the request rate is 1 * factor.

Change-Id: Ia47a8cea80441e51112715f14410d23e8c8fa00a
Signed-off-by: Tianyi Gou <tgou@codeaurora.org>