sparc: explicitly set PCI_IOBASE to 0

Instead of relying on the fallback in asm-generic/io.h which sets
PCI_IOBASE 0 if it is not defined set it explicitly.

Link: https://lore.kernel.org/lkml/CAK8P3a3PK9zyeP4ymELtc2ZYnymECoACiigw9Za+pvSJpCk5=g@mail.gmail.com/
Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>

arch/sparc/include/asm/io.h

@@ -1,6 +1,10 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 #ifndef ___ASM_SPARC_IO_H
 #define ___ASM_SPARC_IO_H
+
+/* On LEON I/O Space is accessed through low iomem */
+#define PCI_IOBASE ((void __iomem *)0)
+
 #if defined(__sparc__) && defined(__arch64__)
 #include <asm/io_64.h>
 #else