MIPS: JZ4770: Work around config2 misreporting associativity

MIPS: JZ4770: Work around config2 misreporting associativity

According to config2, the associativity would be 5-ways, but the
documentation states 4-ways, which also matches the documented
L2 cache size of 256 kB.

Signed-off-by: Maarten ter Huurne <maarten@treewalker.org>
Reviewed-by: James Hogan <jhogan@kernel.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/18488/
Signed-off-by: James Hogan <jhogan@kernel.org>