UBI: fix error path in __wl_get_peb
UBI: fix error path in __wl_get_peb

In case of an error (if there are not free PEB's for example),
__wl_get_peb will return a negative value. In order to prevent access
violation we need to test the returned value prior to using it later on.

Signed-off-by: Tatyana Brokhman <c7fa93ff364b50c0a977a853487528f982a1ac48@codeaurora.org>
Reviewed-by: Dolev Raviv <3d75773ad3271f97975e35fbf4c96b1bb9f3e9d6@codeaurora.org>
Acked-by: Richard Weinberger <320bca71fc381a4a025636043ca86e734e31cf8b@nod.at>
Signed-off-by: Artem Bityutskiy <2f96f8cd3e2780a209d0ab27d1b44624d0019d3f@linux.intel.com>

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