mmc: sdhci-msm: Fix issue with MSM bus bandwidth voting

The driver is using wrong clock rate to calculate the required
bandwidth and due to this voting is happening for more bandwidth
than it is required. This is ultimately preventing system core
voltage from entering into low power mode.

The sdhci_host clock indicates the clock rate as requested by MMC
core layer and the actual rate that is set is indicated by clk_rate
within struct sdhci_msm_host.  As of now, sdhci_host clock is being
used to calculate the bandwidth whereas bus-bw-vectors-bps indicates
only supported bandwidths and hence a mismatch. Fix this by using the
right clock rate which is clk_rate within struct sdhci_msm_host.

Change-Id: If7d81e44a9b479c4c8e9fbaa7e092af2afb9cb9f
Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>