[MIPS] Remove unreferenced _IOC_SLMASK macro in ioctl.h.

Delete the definition of the apparently unreferenced macro _IOC_SLMASK.
Signed-off-by: Robert P. J. Day <rpjday@mindspring.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

include/asm-mips/ioctl.h

@@ -37,11 +37,6 @@
 #define _IOC_SIZESHIFT	(_IOC_TYPESHIFT+_IOC_TYPEBITS)
 #define _IOC_DIRSHIFT	(_IOC_SIZESHIFT+_IOC_SIZEBITS)
 
-/*
- * We to additionally limit parameters to a maximum 255 bytes.
- */
-#define _IOC_SLMASK	0xff
-
 /*
  * Direction bits _IOC_NONE could be 0, but OSF/1 gives it a bit.
  * And this turns out useful to catch old ioctl numbers in header