fix __WORDSIZE on x32 sys/user.h

sys/reg.h already had it right as 32, to which it was explicitly
changed when commit 664cd341 derived
x32 from x86_64. but the copy exposed in sys/user.h was missed.

arch/x32/bits/user.h

 #undef __WORDSIZE
-#define __WORDSIZE 64
+#define __WORDSIZE 32
 
 typedef struct user_fpregs_struct {
 	uint16_t cwd, swd, ftw, fop;