xtensa: Fix linker script patch-up

xtensa: Fix linker script patch-up

The Xtensa architecture requires to patch the generated linker script
to insert precede certain sections with a .literal section. Ammend the
sed script to fix-up only sequences that start with a '*':
'*(.init.text)' -> '*(.init.literal .init.text)'

Signed-off-by: Chris Zankel <chris@zankel.net>