msm_fb: Use clk_set_rate() to vote on ebi_clk rates

clk_set_rate() and clk_set_min_rate() share a common implementation
for ebi_clk, but the clk_set_min_rate() API will soon be eliminated.
Remove its use in preparation for this.

Change-Id: I5a4a4a2f5e2e0ba4989bc7c1f9423653bec0af0f
Signed-off-by: Matt Wagantall <mattw@codeaurora.org>