drivers/nfc/pn544.c: add missing regulator

The regulator framework is used for power management.  The regulators are
only named in the driver code, the actual control stuff is in the board
file for each architecture or use case.

The PN544 chip has three regulators that can be controlled or not -
depending on the architecture where the chip is being used.  So some of
the regulators may not be controllable.  In our current case the third
regulator, which was missing from the code, went unnoticed because we
didn't need to control it.  To be as general as possible - in this respect
- the driver needs to list all regulators.  Then the board file can be
used to actually set the usage.

Signed-off-by: Matti J. Aaltonen <matti.j.aaltonen@nokia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>