um: elf.h: Fix W=1 warning for empty body in 'do' statement

Use the common kernel style to eliminate a warning:

./arch/x86/um/asm/elf.h:215:32: warning: suggest braces around empty body in ‘do’ statement [-Wempty-body]
 #define SET_PERSONALITY(ex) do ; while(0)
                                ^
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Cc: linux-um@lists.infradead.org
Signed-off-by: Richard Weinberger <richard@nod.at>

arch/x86/um/asm/elf.h

@@ -212,6 +212,6 @@ extern int elf_core_copy_fpregs(struct task_struct *t, elf_fpregset_t *fpu);
 extern long elf_aux_hwcap;
 #define ELF_HWCAP (elf_aux_hwcap)
 
-#define SET_PERSONALITY(ex) do ; while(0)
+#define SET_PERSONALITY(ex) do {} while(0)
 
 #endif