sony_pi: Remove the BKL from open and ioctl

The BKL is in this function because of the BKL pushdown (see commit
f8f2c79d

)

It is not needed here because the mutex_lock sonypi_device.lock provides
the necessary locking.

sonypi_misc_ioctl can be converted to unlocked ioctls since it relies on
its own locking (the mutex sonypi_device.lock) and not the bkl

Document that llseek is not needed by explictly setting it to no_llseek

LKML-Reference: <alpine.LFD.2.00.0910192019420.3563@localhost.localdomain>
Signed-off-by: John Kacur <jkacur@redhat.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>