gdb/jit: return bool in jit_breakpoint_re_set_internal and jit_read_descriptor

gdb/jit: return bool in jit_breakpoint_re_set_internal and jit_read_descriptor

This is a minor refactoring that converts the return type of
jit_read_descriptor and jit_breakpoint_re_set_internal functions
from 'int' to 'bool'.

The return value logic of jit_breakpoint_re_set_internal has been
reversed.  With this patch it now returns true if the jit breakpoint
has been successfully initialized.

gdb/ChangeLog:
2020-06-22  Tankut Baris Aktemur  <tankut.baris.aktemur@intel.com>

	* jit.c (jit_read_descriptor): Use bool as the return type.
	(jit_breakpoint_re_set_internal): Use bool as the return type.
	Invert the return value logic; return true if the jit breakpoint
	has been successfully initialized.
	(jit_inferior_init): Update the call to
	jit_breakpoint_re_set_internal.