rcu-tasks: Simplify trc_inspect_reader() QS logic

Currently, trc_inspect_reader() does one check for nesting less than
or equal to zero, then sorts out the distinctions within this single
"if" statement.  This commit simplifies the logic by providing one
"if" statement for quiescent states (nesting of zero) and another "if"
statement for transitioning from one nesting level to another or the
outermost rcu_read_unlock_trace() (negative nesting).

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Neeraj Upadhyay <quic_neeraju@quicinc.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Martin KaFai Lau <kafai@fb.com>
Cc: KP Singh <kpsingh@kernel.org>