ficl on i386 should cast to unsigned char output to support efi i386

make it possible for efi_console to recognize and translate box characters
on i386 build (unsigned versus signed char passed as int issue).

Submitted by:	Toomas Soome <tsoome at me.com>
Reviewed by:	emaste, smh, dteske
MFC after:	3 days
Differential Revision:	https://reviews.freebsd.org/D4993

sys/boot/ficl/i386/sysdep.c

@@ -58,7 +58,7 @@ void  ficlTextOut(FICL_VM *pVM, char *msg, int fNewline)
     IGNORE(pVM);
 
     while(*msg != 0)
-	putchar(*(msg++));
+	putchar((unsigned char)*(msg++));
     if (fNewline)
 	putchar('\n');