msm: pcie: add clk reset assert

Before de-asserting clock reset, PCIe bus driver
needs to assert it first. Add the clock reset
assert call in PCIe bus driver.

Change-Id: Iaec42b8c0c995438d0649101a25affe2029f5a88
Signed-off-by: Tony Truong <truong@codeaurora.org>