test_maple_tree: add the missing MODULE_DESCRIPTION() macro

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

Add the missing invocation of the MODULE_DESCRIPTION() macro.

Link: https://lkml.kernel.org/r/20240531-md-lib-test_maple_tree-v1-1-7b1b485aeec3@quicinc.com


Signed-off-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>