kernel: reorder Z_MEM_SLAB_INITIALIZER() initializers

Trivial change for C++, reorder Z_MEM_SLAB_INITIALIZER members
initialization in the same order they are defined in k_mem_slab
structure.

Fixes #38219

Signed-off-by: Lucas Dietrich <[email protected]>

Author: lucasdietrich

include/kernel.h

@@ -4772,8 +4772,8 @@ struct k_mem_slab {
 #define Z_MEM_SLAB_INITIALIZER(obj, slab_buffer, slab_block_size, \
 			       slab_num_blocks) \
 	{ \
-	.lock = {}, \
 	.wait_q = Z_WAIT_Q_INIT(&obj.wait_q), \
+	.lock = {}, \
 	.num_blocks = slab_num_blocks, \
 	.block_size = slab_block_size, \
 	.buffer = slab_buffer, \