tools/testing/nvdimm: Make symbol '__nfit_test_ioremap' static

The sparse tool complains as follows:

tools/testing/nvdimm/test/iomap.c:65:14: warning:
symbol '__nfit_test_ioremap' was not declared. Should it be static?

This symbol is not used outside of iomap.c, so this
commit marks it static.

Reported-by: Hulk Robot <[e-mail]>
Signed-off-by: Zou Wei <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Dan Williams <[e-mail]>

tools/testing/nvdimm/test/iomap.c

···
 }
 EXPORT_SYMBOL(get_nfit_res);
 
-void __iomem *__nfit_test_ioremap(resource_size_t offset, unsigned long size,
+static void __iomem *__nfit_test_ioremap(resource_size_t offset, unsigned long size,
 		void __iomem *(*fallback_fn)(resource_size_t, unsigned long))
 {
 	struct nfit_test_resource *nfit_res = get_nfit_res(offset);