build: remove clang unused variable increments warnings

Change-Id: Ib755474aa46f7233495fae1947bc27cd0b2d6b4f
Signed-off-by: Spencer Oliver <spen@spen-soft.co.uk>
Reviewed-on: http://openocd.zylin.com/599
Tested-by: jenkins
Reviewed-by: Freddie Chopin <freddie.chopin@gmail.com>

src/flash/nor/at91sam3.c

@@ -3274,7 +3274,6 @@ static int sam3_write(struct flash_bank *bank,
 		r = sam3_page_write(pPrivate, page_cur, pagebuffer);
 		if (r != ERROR_OK)
 			goto done;
-		buffer += count;
 	}
 	LOG_DEBUG("Done!");
 	r = ERROR_OK;

src/flash/nor/at91sam4.c

@@ -2066,7 +2066,6 @@ static int sam4_write(struct flash_bank *bank,
 		r = sam4_page_write(pPrivate, page_cur, pagebuffer);
 		if (r != ERROR_OK)
 			goto done;
-		buffer += count;
 	}
 	LOG_DEBUG("Done!");
 	r = ERROR_OK;