gpio: brcmstb: Make really use of the new lockdep class

gpio: brcmstb: Make really use of the new lockdep class

The recent extension of irq_set_lockdep_class() with a second argument
added the new lockdep class to the mrcmstb driver, but used the already
existing lockdep class as second argument, which leaves the new lockdep
class defined but unused.

Use the new lockdep class as that's what the change intended to do.

Fixes: 39c3fd58952d ("kernel/irq: Extend lockdep class for request mutex")
Reported-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andrew Lunn <andrew@lunn.ch>
Cc: linus.walleij@linaro.org