MIPS: futex: Restore \n after sync instructions

Commit 3c1d3f09 ("MIPS: futex: Emit Loongson3 sync workarounds
within asm") inadvertently removed the newlines following
__WEAK_LLSC_MB, which causes build failures for configurations in which
__WEAK_LLSC_MB expands to a sync instruction:

  {standard input}: Assembler messages:
  {standard input}:9346: Error: symbol `sync3' is already defined
  {standard input}:9380: Error: symbol `sync3' is already defined
  ...

Fix this by restoring the newlines to separate the sync instruction from
anything following it (such as the 3: label), preventing inadvertent
concatenation.

Signed-off-by: Paul Burton <paul.burton@mips.com>
Fixes: 3c1d3f09 ("MIPS: futex: Emit Loongson3 sync workarounds within asm")