libgcc: Fix eh_frame fast path in find_fde_tail

The eh_frame value is only used by linear_search_fdes, not the binary
search directly in find_fde_tail, so the bug is not immediately
apparent with most programs.

Fixes commit e724b048 ("libgcc:
Special-case BFD ld unwind table encodings in find_fde_tail").

libgcc/

	PR libgcc/109712
	* unwind-dw2-fde-dip.c (find_fde_tail): Correct fast path for
	parsing eh_frame.

(cherry picked from commit 49310a99)