ArmVirtPkg DxeHobLib: Update func header description of BuildFv(2)Hob()

ArmVirtPkg DxeHobLib: Update func header description of BuildFv(2)Hob()

Update the function header description of BuildFv(2)Hob() to match
with HobLib.h in MdePkg.

Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=205

Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Regression-tested-by: Laszlo Ersek <lersek@redhat.com>