cosmetics: normalize include guards

use the recommended format [1] of:
<PROJECT>_<PATH>_<FILE>_H_

[1] https://google.github.io/styleguide/cppguide.html#The__define_Guard
"All header files should have #define guards to prevent multiple
inclusion. The format of the symbol name should be
<PROJECT>_<PATH>_<FILE>_H_."

Change-Id: I00a0595fc2a5fc736ab6ff3215727d6db05b10e1
diff --git a/aom_dsp/x86/masked_sad_intrin_ssse3.h b/aom_dsp/x86/masked_sad_intrin_ssse3.h
index 5a2b9e5..cffbd96 100644
--- a/aom_dsp/x86/masked_sad_intrin_ssse3.h
+++ b/aom_dsp/x86/masked_sad_intrin_ssse3.h
@@ -9,8 +9,8 @@
  * PATENTS file, you can obtain it at www.aomedia.org/license/patent.
  */
 
-#ifndef AOM_DSP_X86_MASKED_SAD_INTRIN_SSSE3_H
-#define AOM_DSP_X86_MASKED_SAD_INTRIN_SSSE3_H
+#ifndef AOM_AOM_DSP_X86_MASKED_SAD_INTRIN_SSSE3_H_
+#define AOM_AOM_DSP_X86_MASKED_SAD_INTRIN_SSSE3_H_
 
 unsigned int aom_masked_sad8xh_ssse3(const uint8_t *src_ptr, int src_stride,
                                      const uint8_t *a_ptr, int a_stride,
@@ -30,4 +30,4 @@
                                             const uint8_t *m_ptr, int m_stride,
                                             int height);
 
-#endif  // AOM_DSP_X86_MASKED_SAD_INTRIN_SSSE3_H
+#endif  // AOM_AOM_DSP_X86_MASKED_SAD_INTRIN_SSSE3_H_