pstore: clarify clearing of _read_cnt in ramoops_context

*_read_cnt in ramoops_context need to be cleared during pstore ->open to
support mutli times getting the records.  The patch added missed
ftrace_read_cnt clearing and removed duplicate clearing in ramoops_probe.
Signed-off-by: Liu ShuoX <shuox.liu@intel.com>
Cc: "Zhang, Yanmin" <yanmin_zhang@linux.intel.com>
Cc: Colin Cross <ccross@android.com>
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Tony Luck <tony.luck@intel.com>

fs/pstore/ram.c

@@ -86,6 +86,7 @@ struct ramoops_context {
 	struct persistent_ram_ecc_info ecc_info;
 	unsigned int max_dump_cnt;
 	unsigned int dump_write_cnt;
+	/* _read_cnt need clear on ramoops_pstore_open */
 	unsigned int dump_read_cnt;
 	unsigned int console_read_cnt;
 	unsigned int ftrace_read_cnt;
@@ -101,6 +102,7 @@ static int ramoops_pstore_open(struct pstore_info *psi)
 
 	cxt->dump_read_cnt = 0;
 	cxt->console_read_cnt = 0;
+	cxt->ftrace_read_cnt = 0;
 	return 0;
 }
 
@@ -428,7 +430,6 @@ static int ramoops_probe(struct platform_device *pdev)
 	if (pdata->ftrace_size && !is_power_of_2(pdata->ftrace_size))
 		pdata->ftrace_size = rounddown_pow_of_two(pdata->ftrace_size);
 
-	cxt->dump_read_cnt = 0;
 	cxt->size = pdata->mem_size;
 	cxt->phys_addr = pdata->mem_address;
 	cxt->record_size = pdata->record_size;