um: Make the definition of cpu_data more compatible

Match the x86 implementation to improve build errors.
Noticed when building allyesconfig.

e.g.
../arch/um/include/asm/processor-generic.h:94:19: error: called object is not a function or function pointer
   94 | #define cpu_data (&boot_cpu_data)
      |                  ~^~~~~~~~~~~~~~~
../drivers/gpu/drm/amd/amdgpu/../amdkfd/kfd_topology.c:2157:16: note: in expansion of macro ‘cpu_data’
 2157 |         return cpu_data(first_cpu_of_numa_node).apicid;
Signed-off-by: Peter Foley <pefoley2@pefoley.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

arch/um/include/asm/processor-generic.h

@@ -91,7 +91,7 @@ struct cpuinfo_um {
 
 extern struct cpuinfo_um boot_cpu_data;
 
-#define cpu_data (&boot_cpu_data)
+#define cpu_data(cpu)    boot_cpu_data
 #define current_cpu_data boot_cpu_data
 #define cache_line_size()	(boot_cpu_data.cache_alignment)
 

arch/um/kernel/um_arch.c

@@ -96,7 +96,7 @@ static int show_cpuinfo(struct seq_file *m, void *v)
 
 static void *c_start(struct seq_file *m, loff_t *pos)
 {
-	return *pos < nr_cpu_ids ? cpu_data + *pos : NULL;
+	return *pos < nr_cpu_ids ? &boot_cpu_data + *pos : NULL;
 }
 
 static void *c_next(struct seq_file *m, void *v, loff_t *pos)