cdc: fix line_coding aligment

While calling tud_cdc_n_get_line_coding, the structure is copied into
the destination.

Dump of assembler code for function tud_cdc_n_get_line_coding:
   0x000193f4 <+0>:	mov.w	r2, hathach#2112	@ 0x840
0x000193f8 <+4>:	ldr	r3, [pc, hathach#20]	@ (0x19410
<tud_cdc_n_get_line_coding+28>)
   0x000193fa <+6>:	mla	r0, r2, r0, r3
=> 0x000193fe <+10>:	ldr.w	r3, [r0, hathach#6]
   0x00019402 <+14>:	str	r3, [r1, #0]

On some platform (tested on LPC55S28), the address needs to be 4-bytes
aligned. Without this, the address is

(gdb) p &_cdcd_itf.line_coding
$3 = (cdc_line_coding_t *) 0x40100006 <_cdcd_itf+6>

which leads to a HardFault. With this fix

(gdb) p &_cdcd_itf.line_coding
$5 = (cdc_line_coding_t *) 0x40100008 <_cdcd_itf+8>

and the function can be called properly

Signed-off-by: Jean-Baptiste Theou <[email protected]>

Author: Jean-Baptiste Theou

src/class/cdc/cdc_device.c

@@ -53,7 +53,7 @@ typedef struct
 
   /*------------- From this point, data is not cleared by bus reset -------------*/
   char    wanted_char;
-  cdc_line_coding_t line_coding;
+  CFG_TUSB_MEM_ALIGN cdc_line_coding_t line_coding;
 
   // FIFO
   tu_fifo_t rx_ff;