util: fix MSVC warning in u_align_u32()
util: fix MSVC warning in u_align_u32()

To silence
C:\Users\Brian\projects\mesa\src\util/u_vector.h(41) : warning C4146: unary
minus operator applied to unsigned type, result still unsigned

Reviewed-by: Jose Fonseca <61b5a29db2c0650f7c8510f93eece059c1b09320@vmware.com>
Reviewed-by: Emil Velikov <4c996f2f093ddd0585a556460b4cc3ba555546ef@gmail.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler