breakpoint.c: fix -Wpointer-sign

breakpoint.c: fix -Wpointer-sign

$ make WERROR_CFLAGS="-Wpointer-sign -Werror" breakpoint.o 2>&1 1>/dev/null
../../src/gdb/breakpoint.c: In function ‘breakpoint_xfer_memory’:
../../src/gdb/breakpoint.c:1578:2: error: pointer targets in passing argument 3 of ‘gdbarch_breakpoint_from_pc’ differ in signedness [-Werror=pointer-sign]
In file included from ../../src/gdb/defs.h:644:0,
                 from ../../src/gdb/breakpoint.c:20:
../../src/gdb/gdbarch.h:495:25: note: expected ‘int *’ but argument is of type ‘unsigned int *’

target_info.placed_size is an 'int', and gdbarch_breakpoint_from_pc
takes an int too.

gdb/
2013-03-07  Pedro Alves  <palves@redhat.com>

	* breakpoint.c.c (breakpoint_xfer_memory): Change type of local to
	int.