Fix S32_D32_constX_shaderproc assert

After https://crrev.com/1642273002, fFilterOneY includes a rounding bias
which is not accounted for in the debug-mode S32_D32_constX_shaderproc
check.

Update the S32_D32_constX_shaderproc assert to use the (biased)
SkBitmapProcStateAutoMapper utility.

GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1655823002
R=reed@google.com
BUG=skia:4874

Review URL: https://codereview.chromium.org/1655823002
1 file changed