MIPS: Separate two consecutive loads in memset.S

partial_fixup is used in noreorder block.

Separating two consecutive loads can save one cycle on processors with
GPR intrelock and can fix load-use on processors that need a load delay slot.

Also do so for fwd_fixup.

[Ralf: Only R2000/R3000 class processors are lacking the the load-user
interlock and even some of those got it retrofitted.  With R2000/R3000
being fairly uncommon these days the impact of this bug should be minor.]

Signed-off-by: Tony Wu <tung7970@gmail.com>
To: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/1768/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>