Building for ARM64 leads to the following build warning:

In file included from drivers/staging/dgap/dgap.c:66:0:
drivers/staging/dgap/dgap.h:124:0: warning: "PCI_IO_SIZE" redefined
 #define PCI_IO_SIZE  0x00200000
 ^
In file included from ./arch/arm64/include/asm/page.h:66:0,
                 from include/linux/mm_types.h:15,
                 from include/linux/sched.h:27,
                 from ./arch/arm64/include/asm/compat.h:25,
                 from ./arch/arm64/include/asm/stat.h:23,
                 from include/linux/stat.h:5,
                 from include/linux/module.h:10,
                 from drivers/staging/dgap/dgap.c:47:
./arch/arm64/include/asm/memory.h:39:0: note: this is the location of the previous definition
 #define PCI_IO_SIZE  SZ_16M
 ^

Use PCI_IO_SIZE_DGAP to avoid the name collision.

Reported-by: Olof's autobuilder <build@lixom.net>
Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>