MIPS: Random whitespace clean-ups

Another whitespace clean-up, this removes tabs from between sentences in
some comments.
Signed-off-by: NMaciej W. Rozycki <macro@codesourcery.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/6103/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>