HID: picoLCD: satify some checkpatch warnings

WARNING: static const char * array should probably be static const char * const
+static const char *error_codes[] = {

WARNING: min() should probably be min_t(size_t, 20, s)
+       raw_data[2] = min((size_t)20, s);

Note: the second min_t suggestion cannot be followed because GCC is not
smart enough to track constants through it and make
copy_from_user_overflow() check happy.

WARNING: min() should probably be min_t(u8, 20, raw_data[2])
+       if (copy_from_user(raw_data+3, u, min((u8)20, raw_data[2])))
                return -EFAULT;

Signed-off-by: Bruno Prémont <bonbons@linux-vserver.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>