catalog_read() implements the read interface for the sysfs file

	/sys/bus/event_source/devices/hv_24x7/interface/catalog

It essentially takes a buffer, an offset and count as parameters
to the read() call.  It makes a hypervisor call to read a specific
page from the catalog and copy the required bytes into the given
buffer. Each call to catalog_read() returns at most one 4K page.

Given these requirements, we should be able to simplify the
catalog_read().

diff --git a/arch/powerpc/perf/hv-24x7.c b/arch/powerpc/perf/hv-24x7.c
index 2f2215c..9427ef7 100644
--- a/arch/powerpc/perf/hv-24x7.c
+++ b/arch/powerpc/perf/hv-24x7.c

@@ -185,6 +105,8 @@ static ssize_t catalog_read(struct file *filp, struct kobject *kobj,
 	ssize_t ret = 0;
 	size_t catalog_len = 0, catalog_page_len = 0, page_count = 0;
 	loff_t page_offset = 0;
+	loff_t offset_in_page;
+	size_t copy_len;
 	uint64_t catalog_version_num = 0;
 	void *page = kmem_cache_alloc(hv_page_cache, GFP_USER);
 	struct hv_24x7_catalog_page_0 *page_0 = page;

@@ -203,6 +125,7 @@ static ssize_t catalog_read(struct file *filp, struct kobject *kobj,
 
 	page_offset = offset / 4096;
 	page_count  = count  / 4096;