crypto: caam: Avoid unused imx8m_machine_match variable

If caam module is built without OF support, the compiler returns the
following warning:

	drivers/crypto/caam/ctrl.c:83:34: warning: 'imx8m_machine_match' defined but not used [-Wunused-const-variable=]

imx8m_machine_match is only referenced by of_match_node(), which is set
to NULL if CONFIG_OF is not set, as of commit 5762c20 ("dt: Add
empty of_match_node() macro"):

	#define of_match_node(_matches, _node)  NULL

Do not create imx8m_machine_match if CONFIG_OF is not set.

Reported-by: kernel test robot <[email protected]>
Closes: https://lore.kernel.org/oe-kbuild-all/[email protected]/
Suggested-by: Jakub Kicinski <[email protected]>
Signed-off-by: Breno Leitao <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: leitao

drivers/crypto/caam/ctrl.c

@@ -80,6 +80,7 @@ static void build_deinstantiation_desc(u32 *desc, int handle)
 	append_jump(desc, JUMP_CLASS_CLASS1 | JUMP_TYPE_HALT);
 }
 
+#ifdef CONFIG_OF
 static const struct of_device_id imx8m_machine_match[] = {
 	{ .compatible = "fsl,imx8mm", },
 	{ .compatible = "fsl,imx8mn", },
@@ -88,6 +89,7 @@ static const struct of_device_id imx8m_machine_match[] = {
 	{ .compatible = "fsl,imx8ulp", },
 	{ }
 };
+#endif
 
 /*
  * run_descriptor_deco0 - runs a descriptor on DECO0, under direct control of