libbladeRF: Decreased verbosity of library outputs

In the future, we'll need to standardize the situations in which we use
the log_* functions.  For the time being, it is preferred to err on the
side of less verbosity.

Here's a preliminary list of intended usages:

log_error():
    Unexpected and severe failures.

log_warning():
    Failures and situations that may yield unexpected behavior (e.g.,
    truncation)

log_info(), log_debug(), log_verbose():
    Information about what's going on under the hood. log_info() is the
    least verbose, log_verbose is the most.
libbladeRF, bladeRF-cli: Fixed defects reported by Converity Scan

Addresses CID: 113696 - 1133700, which consist of potential NULL pointer
dereferences, dead code, and invalid memory access (clobbered a NUL
terminator).
host:  CID fixes for ezusb.c - Unchecked return values and user-provided values

Addressing items picked up by the Coverity scan:
    CID 1042551, 1042552, 1042546, 1042537

These items consisted of unchecked return values, and using some
length/size values provided in file headers directly.

Added return value checks and some quick sanity checks on length values.

Did some misc. cleanup on debug output.