msm: mdss: Fix argument in bus scale set quota

Entry MDSS_HW_IOMMU in enum mdss_hw_index is used
as argument in function mdss_bus_scale_set_quota,
but originally the arguments comes from enum
mdss_bus_clients instead of enum mdss_hw_index so
that the array access overflow will happen since
the bus request array is allocated based on the
size of mdss_bus_clients.

Change-Id: I371f6c3ecb4f5723dd9700d5f31155e6dfa4263b
Signed-off-by: Jayant Shekhar <jshekhar@codeaurora.org>
Signed-off-by: Shivaraj Shetty <shivaraj@codeaurora.org>