asm-generic/io.h: Fix sparse warnings on big-endian architectures

On big-endian architectures like OpenRISC, sparse outputs below warnings on
asm-generic/io.h.  This is due to io statements like:

  __raw_writel(cpu_to_le32(value), PCI_IOBASE + addr);

The __raw_writel() function expects native endianness, however
cpu_to_le32() returns __le32.  On little-endian machines these match up
and there is no issue.  However, on big-endian we get warnings, for IO
that is defined as little-endian the mismatch is expected.

The fix I propose is to __force to native endian.

Warnings:

./include/asm-generic/io.h:166:15: warning: cast to restricted __le16
./include/asm-generic/io.h:166:15: warning: cast to restricted __le16
./include/asm-generic/io.h:166:15: warning: cast to restricted __le16
./include/asm-generic/io.h:166:15: warning: cast to restricted __le16
./include/asm-generic/io.h:179:15: warning: cast to restricted __le32
./include/asm-generic/io.h:179:15: warning: cast to restricted __le32
./include/asm-generic/io.h:179:15: warning: cast to restricted __le32
./include/asm-generic/io.h:179:15: warning: cast to restricted __le32
./include/asm-generic/io.h:179:15: warning: cast to restricted __le32
./include/asm-generic/io.h:179:15: warning: cast to restricted __le32
./include/asm-generic/io.h:215:22: warning: incorrect type in argument 1 (different base types)
./include/asm-generic/io.h:215:22:    expected unsigned short [usertype] value
./include/asm-generic/io.h:215:22:    got restricted __le16 [usertype]
./include/asm-generic/io.h:225:22: warning: incorrect type in argument 1 (different base types)
./include/asm-generic/io.h:225:22:    expected unsigned int [usertype] value
./include/asm-generic/io.h:225:22:    got restricted __le32 [usertype]

Signed-off-by: Stafford Horne <shorne@gmail.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>