checkasm/vp9dsp: rename the iszero function to is_zero

Suggested-by: ffmpeg@fb.com
Reviewed-by: Ronald S. Bultje <rsbultje@gmail.com>
Signed-off-by: James Almer <jamrial@gmail.com>

tests/checkasm/vp9dsp.c

@@ -294,7 +294,7 @@ static int copy_subcoefs(int16_t *out, const int16_t *in, enum TxfmMode tx,
     return eob;
 }
 
-static int iszero(const int16_t *c, int sz)
+static int is_zero(const int16_t *c, int sz)
 {
     int n;
 
@@ -362,8 +362,8 @@ static void check_itxfm(void)
                         call_ref(dst0, sz * SIZEOF_PIXEL, subcoef0, eob);
                         call_new(dst1, sz * SIZEOF_PIXEL, subcoef1, eob);
                         if (memcmp(dst0, dst1, sz * sz * SIZEOF_PIXEL) ||
-                            !iszero(subcoef0, sz * sz * SIZEOF_COEF) ||
-                            !iszero(subcoef1, sz * sz * SIZEOF_COEF))
+                            !is_zero(subcoef0, sz * sz * SIZEOF_COEF) ||
+                            !is_zero(subcoef1, sz * sz * SIZEOF_COEF))
                             fail();
 
                         bench_new(dst, sz * SIZEOF_PIXEL, coef, eob);