highbd_sad_sse2.asm: fix xmm count for sad_skip

propagate the xmm argument to the function definitions rather than the
hard coded '7'. some cases use xmm7.

fixes failures on windows of the form:
[ RUN      ] SSE2/SADSkipTest.MaxRef/27
test/register_state_check.h(70): error: Expected equality of these values:
  *xmm_pre
    Which is: 16-byte object <00-00 00-00 00-00 00-00 00-00 00-00 00-00 00-00>
  *xmm_post
    Which is: 16-byte object <FF-00 FF-00 FF-00 FF-00 FF-00 FF-00 FF-00 FF-00>
xmm7 has been modified!

Bug: aomedia:3273
Bug: aomedia:3175
Fixed: aomedia:3175
Change-Id: I10d447de2b4095ee7444f62bba04629bd0abfc02
(cherry picked from commit a3cf693bb1fe85ca0b3677e1c38ff2cbae26a825)
diff --git a/aom_dsp/x86/highbd_sad_sse2.asm b/aom_dsp/x86/highbd_sad_sse2.asm
index a2510d5..48b93bf 100644
--- a/aom_dsp/x86/highbd_sad_sse2.asm
+++ b/aom_dsp/x86/highbd_sad_sse2.asm
@@ -46,9 +46,9 @@
 %endif ; %3 == 5/7
 %else  ; %4 == 2, skip rows
 %if %3 == 5
-cglobal highbd_sad_skip_%1x%2, 4, %3, 7, src, src_stride, ref, ref_stride, n_rows
+cglobal highbd_sad_skip_%1x%2, 4, %3, %5, src, src_stride, ref, ref_stride, n_rows
 %else ; %3 == 7
-cglobal highbd_sad_skip_%1x%2, 4, %3, 7, src, src_stride, ref, ref_stride, \
+cglobal highbd_sad_skip_%1x%2, 4, %3, %5, src, src_stride, ref, ref_stride, \
                             src_stride3, ref_stride3, n_rows
 %endif ; %3 == 5/7
 %endif ; sad/avg/skip