This fixes:

{standard input}: Assembler messages:
{standard input}:145: Error: opcode not supported on this processor: vr5000 (mips4) `clz $2,$2'
{standard input}:920: Error: opcode not supported on this processor: vr5000 (mips4) `clz $7,$9'
{standard input}:1797: Error: opcode not supported on this processor: vr5000 (mips4) `clz $7,$7'
{standard input}:1851: Error: opcode not supported on this processor: vr5000 (mips4) `clz $7,$7'
{standard input}:2831: Error: opcode not supported on this processor: vr5000 (mips4) `clz $7,$7'
{standard input}:4209: Error: opcode not supported on this processor: vr5000 (mips4) `clz $7,$7'
{standard input}:4329: Error: opcode not supported on this processor: vr5000 (mips4) `clz $2,$2'
make[2]: *** [arch/mips/mm/tlbex.o] Error 1

which triggered due to a regression causing the file to be built with
`-march=r5000' rather than `-march=sb1', fixed separately.  Nevertheless
the error should not happen, the other uses of CLZ are appropriately
guarded.  This change copies the arrangement from one of those other
places.
Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/7222/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>