x86[-64]: Fix arch_cpu_user_strlcpy() for small buffers

The case for small buffers was broken, since scasb operates on edi/rdi,
not esi/rsi.

src/system/kernel/arch/x86/32/arch.S

@@ -264,9 +264,12 @@ FUNCTION(arch_cpu_user_strlcpy):
 	/* count remaining bytes in src */
 .L_user_strlcpy_source_count:
 	not		%ecx
+		# %ecx was 0 and is now max
 	xor		%al,%al
+	movl	%esi,%edi
 	repnz
 	scasb
+	movl	%edi,%esi
 
 .L_user_strlcpy_source_done:
 	movl	%esi,%eax

src/system/kernel/arch/x86/64/arch.S

@@ -251,9 +251,12 @@ FUNCTION(arch_cpu_user_strlcpy):
 .L_user_strlcpy_source_count:
 	// Count remaining bytes in src
 	not		%rcx
+		# %rcx was 0 and is now max
 	xor		%al, %al
+	movl	%rsi, %rdi
 	repnz
 	scasb
+	movl	%rdi, %rsi
 
 .L_user_strlcpy_source_done:
 	// Restore the old fault handler