yadif: Fix compiler warning caused by specifying const twice

yadif: Fix compiler warning caused by specifying const twice

  yadif.c:49:24: warning: duplicate 'const' declaration specifier [-Wduplicate-decl-specifier]
  DECLARE_ASM_CONST (16, const xmm_reg, pb_1) = {
                       ^
  yadif.c:33:50: note: expanded from macro 'DECLARE_ASM_CONST'
  #define DECLARE_ASM_CONST(n,t,v)    static const t __attribute__((used)) __attribute__ ((aligned (n))) v
                                                 ^
  yadif.c:52:24: warning: duplicate 'const' declaration specifier [-Wduplicate-decl-specifier]
  DECLARE_ASM_CONST (16, const xmm_reg, pw_1) = {
                       ^
  yadif.c:33:50: note: expanded from macro 'DECLARE_ASM_CONST'
  #define DECLARE_ASM_CONST(n,t,v)    static const t __attribute__((used)) __attribute__ ((aligned (n)))