[packages] valgrind: fix load address handling

[packages] valgrind: fix load address handling
The compile-time generation of the valgrind linker script broke due to toolchain updates
resulting in valgrind binaries compiled with the standard load address of 0x08048000 which
leads to memory conflicts with the debug client later on; valgrind will abort with the
message below:

  valgrind: mmap(0x8048000, 348160) failed in UME with error 22 (Invalid argument).
  valgrind: this can be caused by executables with very large text, data or bss segments.

This change adds another sed pattern to properly substitute the current linker script format.

git-svn-id: svn://svn.openwrt.org/openwrt/packages@28180 3c298f89-4303-0410-b956-a3cf2f4a3e73