gpio/omap: _clear_gpio_irqbank: fix flushing of posted write

In commit 78a1a6d3411de1a8b0dc1cb92754b5f12f251912 (ARM: OMAP4: Update
the GPIO support) braces were mistakenly added to included the
register read-back inside the cpu_is_* checking.

Remove the braces, ensuring that a register read-back is done, even
when the IRQSTATUS2 register is not written.

Note that the register read-back might be IRQSTATUS1 or IRQSTATUS2
depending on the CPU, but a read-back of any register in that region
will cause a flush of the posted writes.

Signed-off-by: Kevin Hilman <khilman@ti.com>