BaseTools: Fix Clang -Wtautological-overlap-compare in PcdValueInit.c

For each structured-PCD field copied via memcpy, DscBuildData.py
emits the clamp expression, '(FieldSize > 0 && FieldSize < ValueSize) ?
FieldSize : ValueSize'. When ValueSize == 1 and FieldSize is unsigned,
it reduces to (FieldSize > 0 && FieldSize < 1) - always-false comparison.

Clang flags it under -Wtautological-overlap-compare, and because
PcdValueInit builds with -Werror, autogen fails and the build aborts with
'PcdValueInit.c: error: overlapping comparisons always evaluate to false
[-Werror,-Wtautological-overlap-compare]'. This is specific to Clang host.

To fix it, this update changes '<' to '<=' at all five generator sites in
DscBuildData.py (GenerateDefaultValueAssignFunction,
GenerateInitValueFunction, GenerateCommandLineValue,
GenerateModuleScopeValue, GenerateFdfValue). Behavior is unchanged:
both branches copy the same byte count when FieldSize == ValueSize.
GCC and MSVC builds are unaffected.

Signed-off-by: Phil Noh <Phil.Noh@amd.com>