BaseTools/GenFfs: Optimazing else if statement

BaseTools/GenFfs: Optimazing else if statement

When Alignment < 0x400 is false, the expression of Alignment >= 0x400 is
always true. So extract the expression from the else if statement.

Cc: Bob Feng <bob.c.feng@intel.com>
Cc: Liming Gao <gaoliming@byosoft.com.cn>
Cc: Yuwei Chen <yuwei.chen@intel.com>
Signed-off-by: Wenyi Xie <xiewenyi2@huawei.com>
Reviewed-by: Bob Feng <bob.c.feng@intel.com>