Input: ff-memless - fix a couple min_t() casts

envelope->attack_level is a u16 type.  We're trying to clamp it here
so it's between 0 and 0x7fff.  Unfortunately, the cast to __s16 turns
all the values larger than 0x7fff into negative numbers and min_t()
thinks they are less than 0x7fff.  envelope_level is an int so now
we've got negative values stored there.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>