selftests/fpu: add missing MODULE_DESCRIPTION() macro

make allmodconfig && make W=1 C=1 now reports:
WARNING: modpost: missing MODULE_DESCRIPTION() in lib/test_fpu.o

Add the missing invocation of the MODULE_DESCRIPTION() macro.

Link: https://lkml.kernel.org/r/20240622-md-i386-lib-test_fpu_glue-v1-1-a4e40b7b1264@quicinc.com
Fixes: 9613736d

 ("selftests/fpu: move FP code to a separate translation unit")
Signed-off-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Reviewed-by: Samuel Holland <samuel.holland@sifive.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>