change inconsistent array param to pointer

The behavior is identical, but the former syntax suggests guarantees that
don't actually exist.

Author: theuni

src/scalar_4x64_impl.h

@@ -681,7 +681,7 @@ static void secp256k1_scalar_reduce_512(secp256k1_scalar *r, const uint64_t *l)
     secp256k1_scalar_reduce(r, c + secp256k1_scalar_check_overflow(r));
 }
 
-static void secp256k1_scalar_mul_512(uint64_t l[8], const secp256k1_scalar *a, const secp256k1_scalar *b) {
+static void secp256k1_scalar_mul_512(uint64_t *l8, const secp256k1_scalar *a, const secp256k1_scalar *b) {
 #ifdef USE_ASM_X86_64
     const uint64_t *pb = b->d;
     __asm__ __volatile__(
@@ -812,7 +812,7 @@ static void secp256k1_scalar_mul_512(uint64_t l[8], const secp256k1_scalar *a, c
     /* Extract l7 */
     "movq %%r8, 56(%%rsi)\n"
     : "+d"(pb)
-    : "S"(l), "D"(a->d)
+    : "S"(l8), "D"(a->d)
     : "rax", "rbx", "rcx", "r8", "r9", "r10", "r11", "r12", "r13", "r14", "r15", "cc", "memory");
 #else
     /* 160 bit accumulator. */