usb: typec: tcpci_maxim: Fix uninitialized return variable

usb: typec: tcpci_maxim: Fix uninitialized return variable

New smatch warnings:
drivers/usb/typec/tcpm/tcpci_maxim.c:324 max_tcpci_irq() error: uninitialized symbol 'irq_return'.
drivers/usb/typec/tcpm/tcpci_maxim.c:407 max_tcpci_probe() warn: passing zero to 'PTR_ERR'

The change fixes the above warnings by initializing irq_return
and replacing IS_ERR_OR_NULL with IS_ERR.

Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Badhri Jagan Sridharan <badhri@google.com>
Link: https://lore.kernel.org/r/20201029063138.1429760-11-badhri@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>