Revert "arch/riscv: Do not use irq_lock() on arch_irq_offload"

This reverts commit b0458201ccd272f4d7e5b7fddbca952f77f67a3c.

The purpose of this commit will be reintroduced later on top of
a cleaner codebase.

Signed-off-by: Nicolas Pitre <npitre@baylibre.com>
diff --git a/arch/riscv/core/irq_offload.c b/arch/riscv/core/irq_offload.c
index a6936f9..22b2243 100644
--- a/arch/riscv/core/irq_offload.c
+++ b/arch/riscv/core/irq_offload.c
@@ -33,8 +33,13 @@
 
 void arch_irq_offload(irq_offload_routine_t routine, const void *parameter)
 {
+	unsigned int key;
+
+	key = irq_lock();
 	_offload_routine = routine;
 	offload_param = parameter;
 
 	__asm__ volatile ("ecall");
+
+	irq_unlock(key);
 }