[MIPS] Fix warnings in run_uncached on 32bit kernel

arch/mips/lib/uncached.c: In function 'run_uncached':
arch/mips/lib/uncached.c:47: warning: comparison is always true due to limited range of data type
arch/mips/lib/uncached.c:48: warning: comparison is always false due to limited range of data type
arch/mips/lib/uncached.c:57: warning: comparison is always true due to limited range of data type
arch/mips/lib/uncached.c:58: warning: comparison is always false due to limited range of data type

Signed-off-by: Yoichi Yuasa <yoichi_yuasa@tripeaks.co.jp>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>