sms: fix CMDA SMS UTF-8 translation

Fixes incoming SMS translation issue seen on MC7354 when translating contents from Latin-1 encoding to UTF-8, because the encoding parameter "ISO−8859−1" used U+2212 (MINUS SIGN) instead of U+002D (HYPHEN-MINUS).

[mm-sms-part-cdma.c:873] read_bearer_data_user_data(): text/data: ignored (latin to UTF-8 conversion error): 0: Conversion from character set 'ISO−8859−1' to 'UTF-8' is not supported

Fix thanks to Peter Hunt