Documentation: devres: add missing entry for devm_platform_ioremap_resource()

devm_platform_ioremap_resource() should be documented in devres.rst.
Add the missing entry.
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20191022084318.22256-2-brgl@bgdev.plSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/driver-api/driver-model/devres.rst

@@ -316,6 +316,7 @@ IOMAP
   devm_ioremap_nocache()
   devm_ioremap_wc()
   devm_ioremap_resource() : checks resource, requests memory region, ioremaps
+  devm_platform_ioremap_resource() : calls devm_ioremap_resource() for platform device
   devm_iounmap()
   pcim_iomap()
   pcim_iomap_regions()	: do request_region() and iomap() on multiple BARs