librtas: sync papr-sysparm.h with kernel

The data member is __u8 as of 8ded03ae48b3
("powerpc/pseries/papr-sysparm: use u8 arrays for payloads").

Verified that the object code in librtas_src/sysparm.o is unchanged by
this.

Signed-off-by: Nathan Lynch <nathanl@linux.ibm.com>
Signed-off-by: Tyrel Datwyler <tyreld@linux.ibm.com>

Author: nathanlynch

librtas_src/papr-sysparm.h

@@ -14,7 +14,7 @@ enum {
 struct papr_sysparm_io_block {
 	__u32 parameter;
 	__u16 length;
-	char data[PAPR_SYSPARM_MAX_OUTPUT];
+	__u8 data[PAPR_SYSPARM_MAX_OUTPUT];
 };
 
 /**