cnss2: Check PCIe link status before dumping registers

There is a chance that PCIe link is not accessible because
either it went into bad state or suspended by the driver.
Check link status before dumping any registers to avoid
unnecessary link access.

Change-Id: Ia2eed5177ff98b3bdf2ebbc0a7ab7d9f8ec3af72
Signed-off-by: Yue Ma <yuem@codeaurora.org>