[bsp][ch32-rsicv][sconscript] add drv_common.c

attach bf4594870e9f8a533450d34a1ea2b4f035e89c96

bsp/wch/risc-v/Libraries/ch32_drivers/SConscript

@@ -1,7 +1,7 @@
 from building import *
 
 cwd = GetCurrentDir()
-src = []
+src = ['drv_common.c']
 path =  [cwd]
 
 if  GetDepend('SOC_RISCV_FAMILY_CH32'):