[thunderx] Fix compilation with older versions of gcc

Remove redundant duplicate typedef which causes a build failure on
older gcc versions.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/drivers/net/thunderxcfg.h

 ///
 /// Protocol structure
 ///
-typedef struct _EFI_THUNDER_CONFIG_PROTOCOL {
+struct _EFI_THUNDER_CONFIG_PROTOCOL {
   EFI_THUNDER_CONFIG_PROTOCOL_GET_CONFIG GetConfig;
   BOARD_CFG* BoardConfig;
-} EFI_THUNDER_CONFIG_PROTOCOL;
+};
 
 #endif /* _THUNDERXCFG_H */