MIPS: Don't try to decode microMIPS branch instructions where they cannot exist.

In mm_isBranchInstr() we can short circuit the entire function if
!cpu_has_mmips.
Signed-off-by: David Daney <david.daney@cavium.com>
Acked-by: Steven J. Hill <Steven.Hill@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/5326/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/math-emu/cp1emu.c

@@ -471,6 +471,9 @@ int mm_isBranchInstr(struct pt_regs *regs, struct mm_decoded_insn dec_insn,
 	unsigned int fcr31;
 	unsigned int bit;
 
+	if (!cpu_has_mmips)
+		return 0;
+
 	switch (insn.mm_i_format.opcode) {
 	case mm_pool32a_op:
 		if ((insn.mm_i_format.simmediate & MM_POOL32A_MINOR_MASK) ==