uqmi: corrected too short received SMS

uqmi: corrected too short received SMS

When characters with ascii values bigger than 0x7f are used, the
length of the received text message is too short.

Test message sent: 123äÄ123
Before correction:
root@OpenWrt:/tmp# uqmi -d /dev/cdc-wdm0 --get-message 20
Raw text: 31 32 33 7b 5b 31 32 33
{
        "smsc": "+46724400001",
        "sender": "+46xxxxxxxxx",
        "timestamp": "2022-03-11 18:48:10",
        "text": "123äÄ1"
}

after correction:
root@OpenWrt:/tmp# uqmi -d /dev/cdc-wdm0 --get-message 20
Raw text: 31 32 33 7b 5b 31 32 33
{
        "smsc": "+46724400001",
        "sender": "+46xxxxxxxxx",
        "timestamp": "2022-03-11 18:48:10",
        "text": "123äÄ123"
}

Signed-off-by: Henrik Ginstmark <henrik@ginstmark.se>