ARC: unwind: Mark expected switch fall-throughs

Mark switch cases where we are expecting to fall through.

This patch fixes the following warnings (Building: haps_hs_defconfig arc):

arch/arc/kernel/unwind.c:827:20: warning: this statement may fall through [-Wimplicit-fallthrough=]
arch/arc/kernel/unwind.c:836:20: warning: this statement may fall through [-Wimplicit-fallthrough=]

Reviewed-by: Kees Cook <[e-mail]>
Signed-off-by: Gustavo A. R. Silva <[e-mail]>
Signed-off-by: Vineet Gupta <[e-mail]>

arch/arc/kernel/unwind.c

···
 			case DW_CFA_def_cfa:
 				state->cfa.reg = get_uleb128(&ptr.p8, end);
 				unw_debug("cfa_def_cfa: r%lu ", state->cfa.reg);
-				/*nobreak*/
+				/* fall through */
 			case DW_CFA_def_cfa_offset:
 				state->cfa.offs = get_uleb128(&ptr.p8, end);
 				unw_debug("cfa_def_cfa_offset: 0x%lx ",
···
 				break;
 			case DW_CFA_def_cfa_sf:
 				state->cfa.reg = get_uleb128(&ptr.p8, end);
-				/*nobreak */
+				/* fall through */
 			case DW_CFA_def_cfa_offset_sf:
 				state->cfa.offs = get_sleb128(&ptr.p8, end)
 				    * state->dataAlign;