common/xz: add comments for the intentionally missing break statements

Signed-off-by: Lasse Collin <lasse.collin@xxxxxxxxxxx>
[Linux commit 84d517f3e56f7d0d305c14a701cee8f7372ebe1e]
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/common/xz/dec_lzma2.c
+++ b/xen/common/xz/dec_lzma2.c
@@ -1043,6 +1043,8 @@ XZ_EXTERN enum xz_ret INIT xz_dec_lzma2_
 
 			s->lzma2.sequence = SEQ_LZMA_PREPARE;
 
+		/* Fall through */
+
 		case SEQ_LZMA_PREPARE:
 			if (s->lzma2.compressed < RC_INIT_BYTES)
 				return XZ_DATA_ERROR;
@@ -1053,6 +1055,8 @@ XZ_EXTERN enum xz_ret INIT xz_dec_lzma2_
 			s->lzma2.compressed -= RC_INIT_BYTES;
 			s->lzma2.sequence = SEQ_LZMA_RUN;
 
+		/* Fall through */
+
 		case SEQ_LZMA_RUN:
 			/*
 			 * Set dictionary limit to indicate how much we want