Patch to fix a couple of compiler warnings from 80a5cf64

The attached patch fixes a couple of compiler warnings seen by the MSVC
build.

contrib\pg_trgm\trgm_regexp.c(234): warning C4305: 'initializing' :
truncation from 'double' to 'const float4' [D:\Postgres\b\pg_trgm.vcxproj]
contrib\pg_trgm\trgm_regexp.c(235): warning C4305: 'initializing' :
truncation from 'double' to 'const float4' [D:\Postgres\b\pg_trgm.vcxproj]

2 Warning(s)

I'm not quite sure why I get 2 warnings rather than 8, but the attached
seems to make them go away, for what it's worth.

Regards

David Rowley