hw/openrisc: Fix masking in openrisc_pic_cpu_handler()

Consider the masking of PICSR and PICMR:

    ((cpu->env.picsr && (1 << i)) && (cpu->env.picmr && (1 << i)))

To correctly mask bits, we should use the bitwise AND "&" rather than
the logical AND "&&".  Also, the loop is not necessary for masking.
Simply use (cpu->env.picsr & cpu->env.picmr).

Signed-off-by: Xi Wang <xi.wang@gmail.com>
Acked-by: Jia Liu <proljc@gmail.com>
