[GDBserver] Don't error in reinsert_raw_breakpoint if bp->inserted

[GDBserver] Don't error in reinsert_raw_breakpoint if bp->inserted

GDBserver steps over a breakpoint while the single step breakpoint
is inserted at the same address, there are two breakpoint objects
using single raw breakpoint, which is inserted (for single step).
When step over is finished, GDBserver reinsert the breakpoint, but
it finds the raw breakpoint is already inserted, and error out
"Breakpoint already inserted at reinsert time."  Even if I change the
order to delete reinsert breakpoints first (which only decreases the
refcount, but leave inserted flag unchanged), the error is still
there.

The fix is to remove the error and return instead.

gdb/gdbserver:

2016-04-25  Yao Qi  <yao.qi@linaro.org>

	* linux-low.c (reinsert_raw_breakpoint): If bp->inserted is true
	return instead of error.