[gdb/testsuite] Fix gdb.guile/scm-symtab.exp for ppc64le

[gdb/testsuite] Fix gdb.guile/scm-symtab.exp for ppc64le

On powerpc64le-linux, I run into:
...
(gdb) PASS: gdb.guile/scm-symtab.exp: step out of func2
guile (print (> (sal-line (find-pc-line (frame-pc (selected-frame)))) line))^M
= #f^M
(gdb) FAIL: gdb.guile/scm-symtab.exp: test find-pc-line with resume address
...

The problem is as follows: the instructions for the call to func2 are:
...
    1000070c:   39 00 00 48     bl      10000744 <func1>
    10000710:   00 00 00 60     nop
    10000714:   59 00 00 48     bl      1000076c <func2>
    10000718:   00 00 00 60     nop
    1000071c:   00 00 20 39     li      r9,0
...
and the corresponding line number info is:
...
scm-symtab.c:
File name     Line number    Starting address    View    Stmt
scm-symtab.c           42          0x1000070c               x
scm-symtab.c           43          0x10000714               x
scm-symtab.c           44          0x1000071c               x
...

The test-case looks at the line numbers for two insns:
- the insn of the call to func2 (0x10000714), and
- the insn after that (0x10000718),
and expects the line number of the latter to be greater than the line number
of the former.

However, both insns have the same line number: 43.

Fix this by replacing ">" with ">=".

Tested on x86_64-linux and powerpc64le-linux.