[MIPS] Remove a duplicated local variable in test_and_clear_bit()

Fix a sparse warning caused by 2c921d07f8c641e691b0dfd80a5cfe14c60ec489

include2/asm/bitops.h:313:23: warning: symbol 'res' shadows an earlier one
include2/asm/bitops.h:309:16: originally declared here

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>