staging: axis-fifo: add unspecified HAS_IOMEM dependency

Currently CONFIG_XIL_AXIS_FIFO=y implicitly depends on
CONFIG_HAS_IOMEM=y; consequently, on architectures without IOMEM we get
the following build error:

ld: drivers/staging/axis-fifo/axis-fifo.o: in function `axis_fifo_probe':
drivers/staging/axis-fifo/axis-fifo.c:809: undefined reference to `devm_ioremap_resource'

Fix the build error by adding the unspecified dependency.

Reported-by: Brendan Higgins <brendanhiggins@google.com>
Signed-off-by: Brendan Higgins <brendanhiggins@google.com>
Link: https://lore.kernel.org/r/20191211192742.95699-7-brendanhiggins@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/axis-fifo/Kconfig

@@ -4,7 +4,7 @@
 #
 config XIL_AXIS_FIFO
 	tristate "Xilinx AXI-Stream FIFO IP core driver"
-	depends on OF
+	depends on OF && HAS_IOMEM
 	help
 	  This adds support for the Xilinx AXI-Stream FIFO IP core driver.
 	  The AXI Streaming FIFO allows memory mapped access to a AXI Streaming