maple_tree: allow TEST_MAPLE_TREE only when DEBUG_KERNEL is set

Prevent a kconfig warning that is caused by TEST_MAPLE_TREE by adding a
"depends on" clause for TEST_MAPLE_TREE since 'select' does not follow any
kconfig dependencies.

WARNING: unmet direct dependencies detected for DEBUG_MAPLE_TREE
  Depends on [n]: DEBUG_KERNEL [=n]
  Selected by [y]:
  - TEST_MAPLE_TREE [=y] && RUNTIME_TESTING_MENU [=y]

Link: https://lkml.kernel.org/r/20221119055117.14094-1-rdunlap@infradead.org
Fixes: 120b1162 ("maple_tree: reorganize testing to restore module testing")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Reported-by: kernel test robot <lkp@intel.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

lib/Kconfig.debug

@@ -2244,6 +2244,7 @@ config TEST_XARRAY
 	tristate "Test the XArray code at runtime"
 
 config TEST_MAPLE_TREE
+	depends on DEBUG_KERNEL
 	select DEBUG_MAPLE_TREE
 	tristate "Test the Maple Tree code at runtime"