tlb_uv.c: Add missing return value check to prevent nptr dereference.

[Jason2031]

Function init_per_cpu() defined in arch/x86/platform/uv/tlb_uv.c calls kzalloc() to allocate memory for variable uvhub_mask which is used in function get_cpu_topology() and function summarize_uvhub_sockets() later. However, none of the 3 functions mentioned above checks whether uvhub_mask is NULL. As kzalloc() may return NULL, when get_cpu_topology() and summarize_uvhub_sockets() tries to dereference this pointer, it may cause NULL pointer dereference bug.

[Jason2031]

Fix bugzilla report 200489.

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