MIPS: atomic: Fix whitespace in ATOMIC_OP macros

We define macros in asm/atomic.h which end each line with space
characters before a backslash to continue on the next line. Remove the
space characters leaving tabs as the whitespace used for conformity with
coding convention.
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@vger.kernel.org
Cc: Huacai Chen <chenhc@lemote.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: linux-kernel@vger.kernel.org