Fix typo in ppc64_standard_linkage7

The ppc64_standard_linkage7 pattern added by Alan's recent patch:
https://sourceware.org/ml/gdb-patches/2013-11/msg00274.html
contains a typo: the ELFv2 TOC slot offset is 24, not 40.
This was correct in the comment, but not the actual code.

ChangeLog:

	* ppc64-tdep.c (ppc64_standard_linkage7): Fix typo.
Fix info-shared.exp testcase to expect the leading `.' found on ppc64's symbols.

gdb/testsuite/
2014-01-28  Edjunior Barbosa Machado  <emachado@linux.vnet.ibm.com>

	* gdb.base/info-shared.exp: Expect leading `.' on ppc64's symbols.