MIPS: kernel: genex: Set correct ISA level

The jr instruction opcode has changed in R6 so make sure
the correct ISA level is set prior using that instruction.
Signed-off-by: NMarkos Chandras <markos.chandras@imgtec.com>

arch/mips/kernel/genex.S

@@ -125,7 +125,7 @@ LEAF(__r4k_wait)
 	nop
 	nop
 #endif
-	.set	arch=r4000
+	.set	MIPS_ISA_ARCH_LEVEL_RAW
 	wait
 	/* end of rollback region (the region size must be power of two) */
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