acpigen: Make acpigen_write_opregion() argument const

This structure is not modified so it can be made const and allow
the calling function to also declare it as a const structure.

Signed-off-by: Duncan Laurie <dlaurie@google.com>
Change-Id: Id8cdfb4b3450a5ab2164ab048497324175b32269
Reviewed-on: https://review.coreboot.org/c/coreboot/+/46258
Reviewed-by: Furquan Shaikh <furquan@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/acpi/acpigen.c

@@ -408,7 +408,7 @@ void acpigen_write_processor_cnot(const unsigned int number_of_cores)
  * len is region length.
  * OperationRegion(regionname, regionspace, regionoffset, regionlength)
  */
-void acpigen_write_opregion(struct opregion *opreg)
+void acpigen_write_opregion(const struct opregion *opreg)
 {
 	/* OpregionOp */
 	acpigen_emit_ext_op(OPREGION_OP);

src/include/acpi/acpigen.h

@@ -429,7 +429,7 @@ void acpigen_write_rom(void *bios, const size_t length);
  * This function takes input region name, region space, region offset & region
  * length.
  */
-void acpigen_write_opregion(struct opregion *opreg);
+void acpigen_write_opregion(const struct opregion *opreg);
 /*
  * Generate ACPI AML code for Mutex
  * This function takes mutex name and initial value.