sparc64: don't treat 64-bit syscall return codes as 32-bit

When checking a system call return code for an error,
linux_sparc_syscall was sign-extending the lower 32-bit value and
comparing it to -ERESTART_RESTARTBLOCK. lseek can return valid return
codes whose lower 32-bits alone would indicate a failure (such as 4G-1).
Use the whole 64-bit value to check for errors. Only the 32-bit path
should sign extend the lower 32-bit value.

Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
Acked-by: Bob Picco <bob.picco@oracle.com>
Acked-by: Allen Pais <allen.pais@oracle.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: sparclinux@vger.kernel.org
Signed-off-by: David S. Miller <davem@davemloft.net>