msm: iommu: Discontinue use of clk_set_min_rate()

Support for the proprietary clk_set_min_rate() API is being removed from
the clock driver. Replace it with a clk_round_rate() and clk_set_rate().

Change-Id: Icd62a8768d99cf007cf899c705626f8eacbaa7c8
Signed-off-by: Matt Wagantall <mattw@codeaurora.org>