OpenBMC: use 0x3a as OEM command for partial add esel

It turns out this is the IBM way to do this and we (OPAL) were just
never really told about the change.

So, with the best public docs that are available being Hostboot
source, let's make the change!

See https://github.com/open-power/hostboot/blob/8e05a4399b/src/include/usr/ipmi/ipmiif.H#L115

Signed-off-by: Stewart Smith <stewart@linux.ibm.com>

platforms/astbmc/common.c

@@ -429,5 +429,5 @@ const struct bmc_platform astbmc_ami = {
 
 const struct bmc_platform astbmc_openbmc = {
 	.name = "OpenBMC",
-	.ipmi_oem_partial_add_esel   = IPMI_CODE(0x32, 0xf0),
+	.ipmi_oem_partial_add_esel   = IPMI_CODE(0x3a, 0xf0),
 };