soc: qcom: qmi_encdec: Restrict string length in decode

The QMI TLV value for strings in a lot of qmi element info structures
account for null terminated strings with MAX_LEN + 1. If a string is
actually MAX_LEN + 1 length, this will cause an out of bounds access
when the NULL character is appended in decoding.

CR-Fixed: 2359244
Change-Id: I4d789bc6017ff58458f77fe875ca4e175a4f1357
Signed-off-by: Chris Lew <clew@codeaurora.org>