staging: iio: meter: add check on return variables
staging: iio: meter: add check on return variables

adds checks on variables that are used to return values. If
the value is less than zero, this indicates that an error
occurred and hence a message is printed through dev_err.
Checks are made on negative values only since spi_* functions
return negative error codes.

The functions were found using the following script but the
aforementioned modification was what was carried out in the end:
@@
identifier len,f;
@@

-int len;
 ... when != len
     when strict
-len =
+return
        f(...);
-return len;

Signed-off-by: Aya Mahfouz <5af60d88056a2c6dcdb35595ae7d607e25785d55@gmail.com>
Reviewed-by: Daniel Baluta <f45a6396254d0683f1df8e14b691f61d753fe117@intel.com>
Signed-off-by: Greg Kroah-Hartman <4645f7897fd33786a2ee1264d590b3c400559d85@linuxfoundation.org>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs