msm: msm_bus: fix count issue in bus rsc handler

Fix an issue where the count for the number of RSCs
in the loop when iterating through to slot in device handles
for the qcom_rpmh rsc devices, this was causing issues
where display rsc device mailbox pointers were not being
populated properly.

Change-Id: I069a9502b07702fb743737ab0e6cfed4b36dcc3f
Signed-off-by: David Dai <daidavid1@codeaurora.org>