msm: clock: Fix rate storage for pll/pll_vote/fixed clocks

pll_clk, pll_vote_clk and fixed_clk have a separate rate field in
their definition structs. This is redundant since the clk struct
embedded in these three clocks has the rate already. In addition,
there is a problem of finding the correct vdd level while update
the vdd for the pll clk which support vdd voting because the level
is found by looking at the rate in the clk struct instead of the
rate outside of clk struct.

Therefore, remove the rate field for these clocks and update the
corresponding get_rate functions.

Change-Id: Iff21488cb7f45447949674ce0bf7543482463bfe
Signed-off-by: Tianyi Gou <tgou@codeaurora.org>