cdef_block_neon.c: Make constrain16 adjdamp parameter signed

The variable is a signed integer at all call sites so adjust the
parameter declaration to match. This avoids MSVC complaining about
negating an unsigned variable.

Bug: aomedia:3507
Change-Id: I8c009c2e3888800f647fa0354ea975e2c1dbe1b3

av1/common/arm/cdef_block_neon.c

diff --git a/av1/common/arm/cdef_block_neon.c b/av1/common/arm/cdef_block_neon.c
index 5e5aa2b..4465e0b 100644
--- a/av1/common/arm/cdef_block_neon.c
+++ b/av1/common/arm/cdef_block_neon.c
@@ -385,8 +385,7 @@
 
 // sign(a-b) * min(abs(a-b), max(0, threshold - (abs(a-b) >> adjdamp)))
 static INLINE int16x8_t constrain16(uint16x8_t a, uint16x8_t b,
-                                    unsigned int threshold,
-                                    unsigned int adjdamp) {
+                                    unsigned int threshold, int adjdamp) {
   int16x8_t diff = vreinterpretq_s16_u16(vsubq_u16(a, b));
   const int16x8_t sign = vshrq_n_s16(diff, 15);
   diff = vabsq_s16(diff);