gpio: pl061: fix probe error handling code

Note that IRQ has not been initialized when kmalloc() fails.

Also, use DECLARE_BITMAP() to make the code clearer.

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Cc: David Brownell <david-b@pacbell.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>