[Coverity][UR] Uninitialized non-static class members

[AlexeySachkov]

See Coverity issues at https://scan.coverity.com/projects/intel-llvm?tab=overview

CID 491850: the following non-static class members are uninitialized:

llvm/unified-runtime/source/adapters/hip/sampler.hpp

Lines 32 to 34 in 8dea47b

	float MinMipmapLevelClamp;
	float MaxMipmapLevelClamp;
	float MaxAnisotropy;

This is a very minor thing, since they are unused, but we should probably still initialize them just in case. Alternatively, we could replace them with a byte-array padding to indicate that those fields exists purely for data type alignment between adapters (which is my current theory)