V4 JIT: fix MSVC warning.
V4 JIT: fix MSVC warning.

d:\dev\qt5-dev\qtdeclarative\src\qml\jit\qv4assembler_p.h(394) : warning C4146: unary minus operator applied to unsigned type, result still unsigned

Change-Id: Iff972f419d7505ecedeb42b4b7eb456295225cb2
Reviewed-by: Simon Hausmann <a975102812d593b3191088e3d0aeaeb6f11dbcf5@digia.com>

qmlc/qtdeclarative,qmlc/qtdeclarative,qmlc/qtdeclarative,qmlc/qtdeclarative,qmlc/qtdeclarative,mgrunditz/qtdeclarative-2d,mgrunditz/qtdeclarative-2d,mgrunditz/qtdeclarative-2d,qmlc/qtdeclarative,mgrunditz/qtdeclarative-2d,qmlc/qtdeclarative,mgrunditz/qtdeclarative-2d,mgrunditz/qtdeclarative-2d,qmlc/qtdeclarative,mgrunditz/qtdeclarative-2d