Darwin: fix bad loop incrementation

Darwin: fix bad loop incrementation

When reading symbols from the vector of oso files on Mac OS X
Darwin, a previous commit introduce a change in the loop and add
an increment at each loop iteration whereas this incrementation is
not needed since the increment or set of the loop control variable
is already done in the loop.

gdb/ChangeLog:

	* machoread.c (macho_symfile_read_all_oso): Remove uneeded
	incrementation.

Change-Id: I3a5a6deb4e9d834ee7d4217a62d90c2ffb7241bc