msm: pcie: check the return value of irq_get_chip_data

The function irq_get_chip_data may return NULL and derefercing it
will throw an exception. This change checks the return value of
irq_get_chip_data and handles it in the case it is NULL.

Change-Id: I4cc2c94aaa8ab87eb3eb925ef8ae7e4ef929fb11
Signed-off-by: Tony Truong <truong@codeaurora.org>