omap: gpio: fix incorrect matching of IRQ_TYPE_EDGE_BOTH

Since IRQ_TYPE_EDGE_BOTH is defined as (IRQ_TYPE_EDGE_FALLING |
IRQ_TYPE_EDGE_RISING), testing against it with a bitwise AND also matches
both single-edge cases in addition to the intended both edges case. Fix it,
replacing with a more accurate expression.

Created and tested againts linux-2.6.34-rc3.
Applicable to 2.6.33-stable as well.

Signed-off-by: Janusz Krzysztofik <jkrzyszt@tis.icnet.pl>
Signed-off-by: Tony Lindgren <tony@atomide.com>