spi: Remove BKL from spidev_open

The BKL was added there with the big pushdown. Remove it as the code
is serialized already.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
LKML-Reference: <20091010153349.318535932@linutronix.de>
Cc: David Brownell <dbrownell@users.sourceforge.net>