Xml backend: Set errno = EINVAL if we can't parse the XML
Xml backend: Set errno = EINVAL if we can't parse the XML

Retrieving the actual error from libxml2 and mapping it to an errno
value is not really possible, so we just set errno to EINVAL upon error.
It's still better than not setting it.

Signed-off-by: Paul Cercueil <73d292422978d45c9eeef455bb1b24a0db453722@analog.com>

analogdevicesinc/libiio,analogdevicesinc/libiio,analogdevicesinc/libiio,analogdevicesinc/libiio