MdeModulePkg/PartitionDxe: Remove unnecessary parentheses in 'if'

MdeModulePkg/PartitionDxe: Remove unnecessary parentheses in 'if'

This commit removes unnecessary parentheses in 'if' statements to
resolve the build failures by the XCODE5 tool chain.

Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Hao Wu <hao.a.wu@intel.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>