dsp.h: fix -Wundef w/__mips_dsp_rev
@@ -93,7 +93,7 @@ extern "C" {
#define WEBP_USE_MIPS32
#if (__mips_isa_rev >= 2)
#define WEBP_USE_MIPS32_R2
-#if defined(__mips_dspr2) || (__mips_dsp_rev >= 2)
+#if defined(__mips_dspr2) || (defined(__mips_dsp_rev) && __mips_dsp_rev >= 2)
#define WEBP_USE_MIPS_DSP_R2
#endif
#endif
