msm: msm_bus: Don't disable bus qos clock unconditionally

When finished programming the QoS registers for a given master belonging
to a bus, don't disable the bus clock unconditionally. Rather disable
the bus clock only if it was enabled as part of setting the QoS registers.

Change-Id: I16e1d72683288b4533a126ecf284ca883aa4981b
Signed-off-by: Girish Mahadevan <girishm@codeaurora.org>