MdeModulePkg/PciBusDxe: Fix possible uninitialized use
    
    If the function gets invalid value for the `ResizableBarOp` parameter
    and asserts are disabled, `Bit` can be used uninitialized.
    
    Cc: Jian J Wang <jian.j.wang@intel.com>
    Cc: Hao A Wu <hao.a.wu@intel.com>
    Cc: Ray Ni <ray.ni@intel.com>
    Signed-off-by: Sergei Dmitrouk <sergei@posteo.net>
    Reviewed-by: Hao A Wu <hao.a.wu@intel.com>