libsrc: fix build warning

CC:  umm_heap/umm_brkaddr.c libsamplerate/src/samplerate.c: In function ‘src_float_to_int_array’:
libsamplerate/src/samplerate.c:468:5: warning: "CPU_CLIPS_POSITIVE" is not defined, evaluates to 0 [-Wundef]
  468 | #if CPU_CLIPS_POSITIVE == 0
      |     ^~~~~~~~~~~~~~~~~~
libsamplerate/src/samplerate.c:474:5: warning: "CPU_CLIPS_NEGATIVE" is not defined, evaluates to 0 [-Wundef]
  474 | #if CPU_CLIPS_NEGATIVE == 0
      |     ^~~~~~~~~~~~~~~~~~

Signed-off-by: shizhenghui <shizhenghui@xiaomi.com>

libs/libc/audio/libsrc/Make.defs

@@ -45,6 +45,8 @@ CFLAGS += -DPACKAGE=\"$(PACKAGE)\" -DVERSION=\"$(VERSION)\"
 
 CFLAGS += ${INCDIR_PREFIX}$(TOPDIR)$(DELIM)include$(DELIM)nuttx$(DELIM)audio
 
+CFLAGS += -DCPU_CLIPS_NEGATIVE=0
+
 ifeq ($(CONFIG_SINC_FAST_CONVERTER),y)
 CFLAGS += -DENABLE_SINC_FAST_CONVERTER
 endif