cnss2: Fix KW issues for pointer check and variable init

Fix KW issues by adding code for pci_priv NULL check before
deference and initialize cnss_reason for MHI_CB_BOOTUP_TIMEOUT
case.

Change-Id: Iab421c62f7cc346b36c4e9ba77403eb5e1923b5a
Signed-off-by: Mohammed Siddiq <msiddiq@codeaurora.org>