remove size suffix in x86_64 __pthread_self asm

the operand size is unnecessary, since the assembler knows it from the
destination register size. removing the suffix makes it so the same
code should work for x32.

arch/x86_64/pthread_arch.h

 static inline struct pthread *__pthread_self()
 {
 	struct pthread *self;
-	__asm__ __volatile__ ("movq %%fs:0,%0" : "=r" (self) );
+	__asm__ __volatile__ ("mov %%fs:0,%0" : "=r" (self) );
 	return self;
 }