meta: Move declaration before code.

meta: Move declaration before code.

Fixes MSVC build.

meta.c(2411) : error C2143: syntax error : missing ';' before 'type'
meta.c(2411) : error C2143: syntax error : missing ')' before 'type'
meta.c(2411) : error C2065: 'layer' : undeclared identifier
meta.c(2411) : error C2059: syntax error : ')'
meta.c(2411) : error C2143: syntax error : missing ';' before '{'
meta.c(2413) : error C2065: 'layer' : undeclared identifier
meta.c(2415) : error C2065: 'layer' : undeclared identifier

Signed-off-by: Vinson Lee <vlee@freedesktop.org>