mmc: host: sdhci-msm-ice: Initialize local variable in ice_cmdq_cfg()

Uninitialized key_index local variable in sdhci_msm_ice_cmdq_cfg() would
be passed as it is to sdhci_msm_ice_hci_update_cmdq_cfg()
/sdhci_msm_ice_update_cfg() when request is not valid. So initialize
this variable with right value.

Without this change, its causing KW warning.

Change-Id: Ibf2f3973e8e2143b303196133758534846437b46
Signed-off-by: Siba Prasad <sibap@codeaurora.org>