staging: dgap: Avoid name collision

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>

drivers/staging/dgap/dgap.c

@@ -2196,7 +2196,7 @@ static struct board_t *dgap_found_board(struct pci_dev *pdev, int id,
 	 * will be mapped into the low 2MB of the 4MB memory space
 	 */
 	brd->port = brd->membase + PCI_IO_OFFSET;
-	brd->port_end = brd->port + PCI_IO_SIZE;
+	brd->port_end = brd->port + PCI_IO_SIZE_DGAP;
 
 	/*
 	 * Special initialization for non-PLX boards

drivers/staging/dgap/dgap.h

@@ -121,7 +121,7 @@
 #define PCI_IO_OFFSET		0x00200000
 
 /* Size of IO (2MB) */
-#define PCI_IO_SIZE		0x00200000
+#define PCI_IO_SIZE_DGAP	0x00200000
 
 /* Number of boards we support at once. */
 #define	MAXBOARDS	32