lib: 842: Improve error handling in sw842_compress()

The static code analysis tool "Coverity Scan" pointed the following
implementation details out for further development considerations:
CID 1309755: Unused value
In sw842_compress: A value assigned to a variable is never used. (CWE-563)
returned_value: Assigning value from add_repeat_template(p, repeat_count)
to ret here, but that stored value is overwritten before it can be used.

Conclusion:
Add error handling for the return value from an add_repeat_template()
call.

Fixes: 2da572c959dd ("lib: add software 842 compression/decompression")
Signed-off-by: Tanya Agarwal <[e-mail]>
Signed-off-by: Herbert Xu <[e-mail]>

lib/842/842_compress.c

···
 		}
 		if (repeat_count) {
 			ret = add_repeat_template(p, repeat_count);
+			if (ret)
+				return ret;
 			repeat_count = 0;
 			if (next == last) /* reached max repeat bits */
 				goto repeat;