[gdb/testsuite] Fix gdb.base/relocate.exp with -readnow

[gdb/testsuite] Fix gdb.base/relocate.exp with -readnow

With test-case gdb.base/relocate.exp and target board readnow, we get:
...
FAIL: gdb.base/relocate.exp: symbol-file with offset
FAIL: gdb.base/relocate.exp: add-symbol-file with offset
FAIL: gdb.base/relocate.exp: add-symbol-file with offset, text address given
FAIL: gdb.base/relocate.exp: add-symbol-file with offset, data address given
...

Fix these FAILs by updating the regexps for -readnow.

Tested on x86_64-linux.

gdb/testsuite/ChangeLog:

2020-10-28  Tom de Vries  <tdevries@suse.de>

	* gdb.base/relocate.exp: Update regexp for -readnow.