powerpc64/ftrace: Drop pointless static qualifier in is_b_op()

There is no need to have the 'intoffset' variable static since new value
always be assigned before use it.

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Reviewed-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>