Fix a type confusion bug in bta_av_setconfig_rej

tBTA_AV_CI_SETCONFIG is treated as tBTA_AV_STR_MSG
in bta_av_setconfig_rej, resulting OOB access.

Bug: 260230151
Test: manual
Ignore-AOSP-First: security
Tag: #security
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:d5ec52732410406d4adf6bab85bb981f836b32dc)
Merged-In: I78a1ee50dea0113381e51f8521711d758dc759cf
Change-Id: I78a1ee50dea0113381e51f8521711d758dc759cf