Bluetooth: Mesh: Avoid undefined behavior in bit shift in blob_cli.c

block_size_log can be 0x20 which will shift 1 by 32 bits which will
cause undefined behavior. Adding ULL to 1 is an option but this will add
little bit more code when debug option is enabled. So simply print the
logarithmic value.

Coverity-ID: 316387
Fixes #58951

Signed-off-by: Pavel Vasilyev <pavel.vasilyev@nordicsemi.no>