nfc: pn544: Fix occasional HW initialization failure

The PN544 driver checks the "enable" polarity during of driver's probe and
it's doing that by turning ON and OFF NFC with different polarities until
enabling succeeds. It takes some time for the hardware to power-down, and
thus, to deassert the IRQ that is raised by turning ON the hardware.
Since the delay after last power-down of the polarity-checking process is
missed in the code, the interrupt may trigger immediately after installing
the IRQ handler (right after the checking is done), which results in IRQ
handler trying to touch the disabled HW and ends with marking NFC as
'DEAD' during of the driver's probe:

  pn544_hci_i2c 1-002a: NFC: nfc_en polarity : active high
  pn544_hci_i2c 1-002a: NFC: invalid len byte
  shdlc: llc_shdlc_recv_frame: NULL Frame -> link is dead

This patch fixes the occasional NFC initialization failure on Nexus 7
device.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>