ia64/perfmon: Convert to unlocked_ioctl

The ioctl function in this driver does not
do anything that requires the BKL, so make
it use unlocked_ioctl.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Tony Luck <tony.luck@intel.com>
Cc: linux-ia64@vger.kernel.org
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>