Typo fix in signal_pass initialization

Typo fix in signal_pass initialization

When I read the code, I happen to see this:

   signal_pass = (unsigned char *)
     xmalloc (sizeof (signal_program[0]) * numsigs);
                      ^^^^^^^^^^^^^^
It is a typo, and this patch is to fix it.

gdb:

2014-06-26  Yao Qi  <yao@codesourcery.com>

	* infrun.c (_initialize_infrun): Replace "signal_program[0]"
	with "signal_pass[0]" in the initialization of signal_pass.