vkd3d-shader/tpf: Return unsigned int from hlsl_sm4_register_from_semantic().

Fix a compile warning:

../vkd3d/libs/vkd3d-shader/hlsl_codegen.c: In function 'allocate_semantic_register': ../vkd3d/libs/vkd3d-shader/hlsl_codegen.c:2947:85: error: passing argument 4 of 'hlsl_sm4_register_from_semantic' from incompatible pointer type [-Werror=incompatible-pointer-types] 2947 | if ((builtin = hlsl_sm4_register_from_semantic(ctx, &var->semantic, output, &type, NULL, &has_idx))) | ^~~~~ | | | unsigned int * In file included from ../vkd3d/libs/vkd3d-shader/hlsl_codegen.c:21: ../vkd3d/libs/vkd3d-shader/hlsl.h:1171:52: note: expected 'enum vkd3d_sm4_register_type *' but argument is of type 'unsigned int *' 1171 | bool output, enum vkd3d_sm4_register_type *type, enum vkd3d_sm4_swizzle_type *swizzle_type, bool *has_idx); | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~