Transceiver52M: Fix SSE preprocessor definition

Using non-SSE4.1 enabled architecture would cause undefined
reference to 'convert_si16_ps' call.

Signed-off-by: Thomas Tsou <tom@tsou.cc>

git-svn-id: http://wush.net/svn/range/software/public/openbts/trunk@6844 19bc5d8c-e614-43d4-8b26-e1612bc8e597